Display device and driving method thereof

ABSTRACT

An array substrate ( 10 ) is provided with a pixel electrode ( 3 ) disposed in a region defined by two adjacent gate wirings ( 1 ) and two adjacent source wirings ( 2 ), a switching element ( 5 ) for switching a voltage applied to the pixel electrode ( 3 ) from the source wiring ( 2 ) based on a signal voltage supplied from the gate wiring ( 1 ), a common wiring ( 8 ) arranged between the two adjacent gate wirings ( 1 ) and a common electrode ( 4 ) being electrically connected to the common wiring ( 8 ) and generating an electric field between the pixel electrode ( 3 ) whereto a voltage is applied, wherein the pixel electrode ( 1 ) comprises a first pixel electrode ( 1   a ) and a second pixel electrode ( 2   a ), and the opposing electrode ( 2 ) comprises a first opposing electrode ( 1   b ) and a second opposing electrode ( 2   b ), wherein a first region generates an electric field between the first pixel electrode ( 1   a ) and the first opposing electrode ( 2   a ) whose light transmittance is lower than that of the first pixel electrode ( 1   a ) and a second region generates an electric field between the second pixel electrode ( 1   b ) and the second opposing electrode ( 2   b ) whose light transmittance is higher than that of the second pixel electrode ( 1   b ) are formed.

TECHNICAL FIELD

The present invention relates to display devices such as liquid crystaldisplay devices, etc., and driving methods thereof.

BACKGROUND ART

Liquid crystal display devices are in wide use as thin and light flatdisplays for use in various electronic machines. There are severaldisplay schemes used in liquid crystal display devices. Among those, ascheme known as IPS (In-Plane Switching), in which an electric field isapplied to liquid crystal in parallel to a substrate for obtaining awide viewing angle, is suitably used for monitor displays for use inpersonal computers, liquid crystal TV sets or the like because of itsexcellent image properties.

Liquid crystal display devices using IPS are disclosed in JapaneseUnexamined Patent Publication No. 10-10556, for example. A plan view ofa pixel portion thereof is shown in FIG. 47. Such a liquid crystaldisplay device comprises an array substrate and an opposing substrateparallel to each other, and liquid crystal held between the arraysubstrate and the opposing substrate. As shown in FIG. 47, in the arraysubstrate, gate wirings 101 feeding scanning signals and source wirings102 feeding image signals are arranged so as to intersect atapproximately right angles. Nearby each intersection of the gate wiring101 and the source wiring 102, a thin-film transistor (TFT) 104 having asemiconductor layer is formed as a switching element. To the sourcewiring 102, a comb-like pixel electrode 115 is connected via the TFT104. Opposing electrodes 116 functioning as a standard potential arearranged so as to mesh with the pixel electrode 115. The opposingelectrodes 116 are electrically connected to a common wiring 103parallel to the gate wiring 101 through a contact hole 108. At theintersection of the common wiring 103 and the pixel electrode 115, withan insulating layer (not shown) in between, a storage capacitor region107 is formed.

According to such a liquid crystal display device, an electric fieldsubstantially parallel to the substrates is generated by the differencebetween the voltage applied to the pixel electrode 115 and that of theopposing electrode 116, to which a standard potential is applied, andthereby the liquid crystal (not shown) held between the electrodes isdriven. By storing electric charge in the storage capacitor region 107while the TFT 104 is in an on-status, the liquid crystal remainsactuated while the TFT 104 is in an off-status.

In prior art IPS style liquid crystal display devices, pixel electrodesand opposing electrodes are generally made of aluminum or the likemetals. Therefore, the pixel electrodes and opposing electrodes do nottransmit light, leading to the drawback of an unsatisfactory pixelaperture ratio. Japanese Unexamined Patent Publication No. 10-10556proposes a way to enhance the aperture ratio by forming either or bothof the pixel electrode 115 and the opposing electrode 116 out of atransparent conductive film.

In the case where both the pixel electrode 115 and the opposingelectrode 116 are made of transparent electrodes, it is preferable thatboth the electrodes be formed as a same layer in order to avoid a morecomplicated production process and increased manufacturing costs.However, this arrangement may lower the manufacturing yield by causingshort-circuits between the pixel electrode 115 and the opposingelectrode 116. Therefore, it is more practical that either the pixelelectrode or the opposing electrode be made of a transparent electrode.

However, forming only one of the pixel electrode and the opposingelectrode out of a transparent electrode and forming the other out ofmetal or a like material may cause flicker due to the difference in theoptical properties of the two materials.

In order to apply a sufficient voltage to liquid crystal molecules whilepreventing decomposition or deterioration thereof, liquid crystaldisplay devices are driven by the alternating current drive method,where an electric potential alternately positive and negative relativeto that of the opposing electrode is applied to the pixel electrode at aregular interval (for example, once every sixtieth seconds). When thealternating current drive method is employed in a liquid crystal displaydevice in which only one of the pixel electrode and the opposingelectrode is a transparent electrode, its transmittance changescyclically between the period when an electric potential positiverelative to that of the opposing electrode (positive frame) is appliedto the pixel electrode and the period when an electric potentialnegative relative to that of the opposing electrode (negative frame) isapplied to the pixel electrode, causing observable differences inbrightness.

DISCLOSURE OF THE INVENTION

The present invention aims to overcome the drawbacks described above. Anobject of the invention is to prevent flicker of a display device inwhich an electro-optic material is driven by applying a voltage betweentwo electrodes having different transmittances.

The inventors conducted research into the causes of the flickerdescribed above and found that the following two factors greatly affectthe occurrence of flicker. A first factor is the flexoelectric effect.The flexoelectric effect is a polarization phenomenon brought about bysplay deformation (orientation deformation) of liquid crystal. Regardingthe relationship between the flexoelectric effect and IPS, “Manuscriptsof Lectures at the 1999 Japanese Liquid Crystal Conference” (page 514,lecture number 3D06) explains the occurrence of domain reversal inconnection with the positive and negative electrodes and rubbingdirection.

How the flexoelectric effect influences flicker will be explained belowwith reference to FIGS. 44( a), 44(b), 44(c) and 44(d). In FIG. 44( a),when a positive voltage is applied to an electrode 21 and a negativevoltage is applied to an electrode 22 in a liquid crystal display deviceusing IPS or the like where a lateral electric field is applied, a solidline 26 represents a line of electric force, when the shape effect ofthe liquid crystal molecules is left out of consideration. On theelectrodes 21 and 22, the lines of electric force splay out. In thisfigure, 23 represents a liquid crystal layer, 24 represents an opposingsubstrate, and 25 represents an array substrate. Liquid crystal displaydevices are driven by the alternating current drive method. Therefore,the direction of the electric field reverses, for example, once everysixtieth of seconds.

FIG. 44( b) shows an array of liquid crystal molecules 27 formed out ofthis splay electric field. To the end of each of the liquid crystalmolecules, a cyano group, a fluorine atom or the like is introduced togive dielectric anisotropy. These parts function as negative electrodesof a dipole moment and compose the larger part of the molecularskeleton. As shown in an enlarged view of FIG. 44( b) (in the circle),the molecule has a wedge-like shape opening to the negative electrodeside. Because of the shape effect (excluded volume effect), when a splayshape alternating electric field is applied to the liquid crystalmolecules, they will tend to be arranged so as to direct the narrowerend of the wedge to the electrode side and the wider end to the centerof the liquid crystal layer. The liquid crystal molecules 27 areuniformly aligned as described above and this generates an electricfield 28 attributable to the liquid crystal molecules. This phenomenonis known as the flexoelectric effect.

FIG. 44( c) illustrates a composite electric field 29 shown by brokenlines which is generated by the original electric field 26 and theelectric field 28 attributable to the flexoelectric effect in the liquidcrystal molecules. The composite electric field 29 exhibits a strongervertical electric field on the positive electrode 21 side and a weakervertical electric field on the negative electrode 22 side.

As a result, its distribution of transmittance varies depending on thepolarity (i.e., positive or negative) of the applied voltage. FIG. 44(d) shows the transmittance distribution when both electrodes 21 and 22are transparent. Here, the solid line shows the transmittancedistribution when the electrode 21 has a positive electric potential(positive frame), and the dash-and-dot line shows the transmittancedistribution when the electrode 21 has a negative electric potential(negative frame). Both electrodes are symmetric with respect to alongitudinal axis passing through the midpoint thereof. Therefore, whenboth electrodes 21 and 22 are transparent or both electrodes 21 and 22have opaque properties, very little variance in the transmittancebetween the positive and negative frames is observed. When one of theelectrodes transmits light and the other blocks light or thetransmittances of the two electrodes 21 and 22 are significantlydifferent, the transmittance of the pixel differs between the positiveand negative frames due to the difference of their optical contributionratios, causing flicker.

A second main factor causing flicker is influence by a peripheralelectric potential. FIG. 45( a) shows equipotential lines when, out ofthe three electrodes 32, 33 and 34 disposed on an array substrate 36, avoltage of −5 volts (V) is applied to the end electrodes 32 and 34 and avoltage of +5 V is applied to the middle electrode 33. When the electricpotential of the interface of opposing substrate 35 is assumed to be theaverage of the two voltages (i.e. 0 V), equipotential lines of 0 V existon the lines normal to the substrate passing through points equidistantto any two adjacent electrodes among 32, 33 and 34. Therefore, when theflexoelectric effect is left out of consideration, the three electrodes32, 33 and 34 are equivalent. Therefore, when the electrode 33 has apositive electric potential and when it has a negative electricpotential, its transmittance distribution is shown by the solid line inFIG. 45( b), and this enables the transmittance of the pixel to remainstable, even when some of the plurality of electrodes 32, 33 and 34is/are made transparent, resulting in no occurrence of flicker.

However, in an IPS style liquid crystal display device, there is noelectrode on the surface of the opposing substrate and this makes itdifficult to form a desirable electric potential on the interface 35.Therefore, if the electric potential of the interface 35 of the opposingsubstrate is assumed to be −5 V, in cases where the electrode 33 has apositive electric potential, as shown in FIG. 46( a), equipotentiallines of −5 V form above electrodes 32 and 34 along the direction normalto the substrate. In this case, the transmittance distribution is asshown by the solid line in FIG. 46( b), i.e., the transmittances on theend of electrodes (negative electrodes) 32 and 34 are higher than thaton the middle electrode (positive electrode) 33. On the other hand, whenthe electrode 33 has a negative electric potential, as shown by thebroken line in FIG. 46( b), the transmittances on the end electrodes(positive electrodes) 32 and 34 become lower than that on the middleelectrode (negative electrode) 33. Therefore, when some of the pluralityof electrodes 32, 33 and 34 is/are made transparent, frames where thetransparent electrode(s) have a negative electric potential becomebrighter than frames where the transparent electrode(s) have a positiveelectric potential, causing flicker.

Taking these phenomena, which are key causes of flicker, intoconsideration, transmittances of individual pixels in prior art displaydevices are not even but exhibit a certain distribution, i.e., thetransmittance distribution varies between when a pixel electrode has apositive electric potential relative to the opposing electrode (positiveframe) and when the pixel electrode has a negative electric potentialrelative to the opposing electrode (negative frame). Therefore, forexample, when the pixel electrode is made of a transparent material andthe opposing electrode is made of an opaque material, the transmittanceof the pixel electrode in either the positive or negative frame becomeshigher than that of the other frame. On the other hand, the opposingelectrode does not transmit light and therefore the transmittance of theopposing electrode does not change between a positive frame and anegative frame. As a result, the transmittance variance between framesof the pixel electrode is observed as a variance in the brightness ofthe whole pixel.

Such a flicker phenomenon is not limited to IPS style liquid crystaldisplay devices but occurs when display devices comprising twoelectrodes having different light transmittances are driven by thealternating current drive method.

To achieve the above object, the display device of the inventioncomprises an array substrate, an opposing substrate facing the arraysubstrate and an electro-optic substance held between the arraysubstrate and the opposing substrate. The array substrate is providedwith a plurality of gate wirings and a plurality of source wiringsintersecting each other, a pixel electrode disposed in each regiondefined by two adjacent gate wirings and two adjacent source wirings, aswitching element for switching a voltage applied to the pixel electrodefrom the source wiring based on a signal voltage supplied from the gatewiring, a common wiring formed between the two adjacent gate wirings andan opposing electrode being electrically connected to the common wiringand generating an electric field for driving the electro-optic substancebetween the opposing electrode and the pixel electrode whereto a voltageis applied. The pixel electrode comprises a first pixel electrode and asecond pixel electrode, and the opposing electrode comprises a firstopposing electrode and a second opposing electrode. A first region isformed in which an electric field is generated between the first pixelelectrode and the first opposing electrode whose light transmittance islower than that of the first pixel electrode. A second region is alsoformed in which an electric field is generated between the second pixelelectrode and the second opposing electrode whose light transmittance ishigher than that of the second pixel electrode. According to thisdisplay device, flicker can be reduced because the flicker polaritiescaused by the variance in transmittance between the pixel electrode andthe opposing electrode can be cancelled between the first region and thesecond.

In the display device, it is preferable that the first region and thesecond region be adjacent to each other.

It is preferable that a voltage is applied to the first pixel electrodeand the second pixel electrode from the same source wiring based on thesignal voltage supplied from the same gate wiring. This makes thepolarities of a voltage applied to the first pixel electrode and secondpixel electrode the same and reliably cancel flicker polarity.

Preferably, the first region and the second region be disposed in thesame dot. This makes it possible to locate the interface of the firstregion and the second region on the common electrode. It is alsopossible to connect the first pixel electrode to the second pixelelectrode and the first opposing electrode to the second opposingelectrode respectively through contact holes formed in the insulatinglayers held in between. Thereby, formation of contact hole in apertureof the display region for connecting different electrode materials(material transformation) becomes unnecessary, enhancing a high apertureratio. It is also possible to arrange the source wiring between thefirst region and the second region. A preferable arrangement is suchthat the switching elements each correspond to the first pixel electrodeand second pixel electrode, respectively. This arrangement reduces adefective ratio of the dot. Furthermore, when a plurality of the firstregions and a plurality of the second regions are formed, it ispreferable that groups of two consecutively identical regions bealternately arranged along the gate wiring and the interface of the thatgroups of two adjacent first regions and the second regions be locatedon the pixel electrode or the opposing electrode. This allows any twoadjacent regions to share the pixel electrode or the opposing electrode,enhancing the aperture ratio.

When a plurality of the first regions and a plurality of the secondregions are formed, it is preferable that the first regions and thesecond regions are arranged in a manner such that the flicker polaritycyclically changes along both the gate wiring and the source wiringbased on the prescribed voltage polarity applied to the first pixelelectrode and the second pixel electrode. This reduces flicker andachieves a uniform display without suffering from vertical or horizontalstrips while in operation. In this case, it is preferable that theflicker polarities be inverted at every dot along both the gate wiringand the source wiring. When a checkerboard pattern or the like isdisplayed, it is preferable the flicker polarities be inverted at everyplurality of dots along both the gate wiring and the source wiring.

It is also possible to arrange the first region and the second region insuch a manner that each region corresponds to a dot or a pixelcomprising three dots of red, green and blue. In both arrangements,flicker reduction can be achieved in a smaller region.

When storage capacitor electrodes electrically connected to the firstpixel electrode and the second pixel electrode are formed and each ofthem is arranged in the first region and the second region, the twostorage capacitor electrodes are disposed on the common electrode or thegate wiring with insulating layers in between to form storage capacitorregions. In this case, it is preferable that the capacities of the twostorage capacitor regions be made substantially the same. This can beachieved by forming the two storage capacitor electrodes out of the samematerial and making their surface areas substantially the same.

The first pixel electrode and the second opposing electrode can be madeof transparent materials and the first opposing electrode and the secondpixel electrode can be made of an opaque material.

It is preferable that the area of the pixel electrode in the aperture ofthe first region and the area of the opposing electrode in the apertureof the second region be made substantially the same, reliably cancelingflicker polarities and enhancing the flicker reduction effect. In thiscase, it is desirable that the transmittances of the first pixelelectrode and the second opposing electrode be approximately the same.Such an arrangement readily be achieved by covering some portion of thefirst opposing electrode or the second pixel electrode with an opaquelayer formed on the opposing substrate for blocking some portion of thearray substrate from light.

It is preferable that a driving voltage having the same polarity isapplied to the first region and the second region.

It is also preferable that first region and the second region havesubstantially the same absolute value of bright difference between thecase where the pixel electrode has a positive electric potentialrelative to the opposing electrode and the case where the pixelelectrode has a negative electric potential relative to the opposingelectrode.

An object of the invention is also achieved by a display devicecomprises an array substrate, an opposing substrate facing the arraysubstrate and an electro-optic substance held between the arraysubstrate and the opposing substrate. The array substrate is providedwith a plurality of gate wirings and a plurality of source wiringsintersecting each other, a pixel electrode disposed in each regiondefined by two adjacent gate wirings and two adjacent source wirings, aswitching element for switching a voltage applied to the pixel electrodefrom the source wiring based on a signal voltage supplied from the gatewiring, a common wiring formed between the two adjacent gate wirings, anopposing electrode being electrically connected to the common wiring andgenerating an electric field for driving the electro-optic substancebetween the opposing electrode and the pixel electrode whereto a voltageis applied and an intermediate electrode disposed between the pixelelectrode and the opposing electrode. The intermediate electrode has atransmittance either higher or lower than both the pixel electrode andthe opposing electrode.

In this display device, it is preferable that the pixel electrode andthe opposing electrode be formed out of the same material, and theintervals between the pixel electrode and the intermediate electrode andbetween the intermediate electrode and the opposing electrode besubstantially the same.

It is preferable that the intermediate electrode be resistivelyconnected to the pixel electrode and the opposing electrode or conductcapacity coupling can be performed.

It is also preferable that the electric potential of the intermediateelectrode becomes the average value of the electric potential of thepixel electrode whereto a voltage is applied and the electric potentialof the opposing electrode which functions as a standard electricpotential.

In the display device described above, it is preferable that theelectro-optic substance be liquid crystal and the voltage applied to thepixel electrode be an alternating voltage.

An object of the invention can be achieved by applying a drive methodfor use in a display device comprising an array substrate, an opposingsubstrate facing the array substrate and an electro-optic substance heldbetween the array substrate and the opposing substrate. The arraysubstrate is provided with a plurality of gate wirings and a pluralityof source wirings intersecting each other, a pixel electrode disposed ineach region defined by two adjacent gate wirings and two adjacent sourcewirings, a switching element for switching a voltage applied to thepixel electrode from the source wiring based on a signal voltagesupplied from the gate wiring, a common wiring formed between the twoadjacent gate wirings and an opposing electrode being electricallyconnected to the common wiring and generating an electric field fordriving the electro-optic substance between the opposing electrode andthe pixel electrode whereto a voltage is applied. The pixel electrodeand the opposing electrode are made of the materials having differenttransmittances. In this drive method, the voltage applied to the pixelelectrode is inverted every predetermined adjacent regions.

In this drive method, the flicker polarities can be canceled between thetwo adjacent regions, reducing flicker.

It is preferable that the predetermined regions be adjacent to eachother in two directions along the gate wiring and the source wiring.

It is also preferable that each predetermined region correspond to a dotor two dots adjacent in a direction either along the gate wiring or thesource wiring.

The predetermined region can correspond to a pixel composed of threedots of red, green and blue or two adjacent pixels each composed ofthree dots of red, green and blue, wherein the any two adjacent pixelsare adjacent to each other in a direction either along the gate wiringor the source wiring.

An object of the invention can be achieved by applying a drive methodfor use in a display device comprising an array substrate, an opposingsubstrate facing the array substrate and an electro-optic substance heldbetween the array substrate and the opposing substrate. The arraysubstrate is provided with a plurality of gate wirings and a pluralityof source wirings intersecting each other, a pixel electrode disposed ineach region defined by two adjacent gate wirings and two adjacent sourcewirings, a switching element for switching a voltage applied to thepixel electrode from the source wiring based on a signal voltagesupplied from the gate wiring, a common wiring formed between the twoadjacent gate wirings and an opposing electrode being electricallyconnected to the common wiring and generating an electric field fordriving the electro-optic substance between the opposing electrode andthe pixel electrode whereto a voltage is applied. The pixel electrodeand the opposing electrode are made of the materials having differenttransmittances. The voltage applied to the pixel electrode is invertedby increasing or decreasing the volume of prescribed brightnesscompensation voltage.

This method for driving a display device makes the brightnessdifferences approximately the same when the polarity of a voltageapplied to the pixel electrode is inverted, reducing flicker.

When both the pixel electrode and the opposing electrode are formed outof transparent electric conductors, this method for driving a displaydevice can be applied to the case where the total area of the pixelelectrode and the total area of the opposing electrode occupying thetransparent portions in the regions are different from each other.

An object of the invention can be achieved by applying a drive methodfor use in a display device comprising an array substrate, an opposingsubstrate facing the array substrate and an electro-optic substance heldbetween the array substrate and the opposing substrate. The arraysubstrate is provided with a plurality of gate wirings and a pluralityof source wirings intersecting each other, a pixel electrode disposed ineach region defined by two adjacent gate wirings and two adjacent sourcewirings, a switching element for switching a voltage applied to thepixel electrode from the source wiring based on a signal voltagesupplied from the gate wiring, a common wiring formed between the twoadjacent gate wirings and an opposing electrode being electricallyconnected to the common wiring and generating an electric field fordriving the electro-optic substance between the opposing electrode andthe pixel electrode whereto a voltage is applied. The pixel electrodecomprises a first pixel electrode and a second pixel electrode, and theopposing electrode comprises a first opposing electrode and a secondopposing electrode. A plurality of first regions generating an electricfield between the first pixel electrode and the first opposing electrodewhose light transmittance is lower than that of the first pixelelectrode are formed; and a plurality of second regions generating anelectric field between the second pixel electrode and the secondopposing electrode whose light transmittance is lower than that of thesecond pixel electrode are formed. A voltage applied to the first pixelelectrode and the second pixel electrode is inverted based on thearrangement cycles of the first region and the second region so as toflicker polarities periodically change along both the gate wiring andthe source wiring.

This drive method can cancel flicker and prevent vertical or horizontalstrips from appearing on a display during operation.

It is preferable that the flicker polarities are inverted at every dotor every plurality of dots along both or either of the gate wiring andthe source wiring.

-   -   In the drive method, it is preferable that the driving frequency        of the voltage applied to the pixel electrode be 60 Hz or higher        for cancel apparent flicker.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing a structure of one dot serving as aminimal display unit of an array substrate in a display device accordingto Embodiment 1 of the present invention.

FIGS. 2( a), 2(b) and 2(c) are sectional views of FIG. 1.

FIGS. 3 and 4 illustrate operations of the structure shown in FIG. 1.

FIG. 5 is a plan view showing a structure of one dot serving as aminimal display unit of an array substrate in a display device accordingto Embodiment 2 of the invention.

FIGS. 6( a), 6(b), 6(c) and 6(d) are sectional views of FIG. 5.

FIG. 7 is a plan view showing a structure of one dot serving as aminimal display unit of an array substrate in a display device accordingto Embodiment 3 of the invention.

FIG. 8 is a plan view showing a structure of one dot serving as aminimal display unit of an array substrate in a display device accordingto Embodiment 4 of the invention.

FIGS. 9( a) and 9(b) are sectional views of FIG. 8.

FIG. 10 is a plan view showing a structure of one dot serving as aminimal display unit of an array substrate in a display device accordingto Embodiment 5 of the invention.

FIGS. 11( a) and 11(b) are sectional views of FIG. 10.

FIGS. 12( a) and 12(b) schematically illustrate arrays of dots.

FIGS. 13( a), 13(b), 13(c), 13(d), 13(e) and 13(f) schematicallyillustrate several methods for inverting a driving voltage.

FIG. 14 is a plan view showing a structure of one dot serving as aminimal display unit of an array substrate in a display device accordingto Embodiment 6 of the invention.

FIGS. 15( a), 15(b) and 15(c) are sectional views of FIG. 14.

FIG. 16 is a plan view showing a structure of one dot serving as aminimal display unit of an array substrate in a display device accordingto Embodiment 7 of the invention.

FIGS. 17( a), 17(b), 17(c) and 17(d) are sectional views of FIG. 16.

FIG. 18 shows the equivalent circuit of the structure shown in FIG. 16.

FIG. 19 is a plan view showing a structure of one dot serving as aminimal display unit of an array substrate in a display device accordingto Embodiment 8 of the invention.

FIGS. 20( a), 20(b), 20(c), and 20(d) are plan views of FIG. 19.

FIG. 21 shows the equivalent circuit of the structure shown in FIG. 19.

FIG. 22 is a plan view showing a modification of the structure shown inFIG. 19.

FIG. 23 is a plan view showing the structures of two adjacent dots on anarray substrate in a display device according to Embodiment 9 of theinvention.

FIGS. 24( a), 24(b) and 24(c) are sectional views of FIG. 23.

FIG. 25 is a plan view showing the structures of two adjacent dots on anarray substrate in a display device according to Embodiment 10 of theinvention.

FIGS. 26( a), 26(b) and 26(c) are sectional views of FIG. 25.

FIG. 27 schematically shows an array of dots in a pixel of a colordisplay device.

FIG. 28 shows schematic structure of a display device according toEmbodiment 11 of the invention.

FIG. 29 schematically shows arrases of dots in two adjacent pixels of adisplay device according to Embodiment 12 of the invention.

FIG. 30 schematically shows arrays of dots in two adjacent pixels of adisplay device according to Embodiment 13 of the invention.

FIGS. 31( a), 31(b), 31(c), 31(d), 31(e) and 31(f) schematically showthe polarities of drive waveforms on odd frames, dot structure andflicker polarities of a display device according to Embodiment 14 of theinvention.

FIGS. 32( a), 32(b), 32(c) and 32(d) schematically show the polaritiesof drive waveforms on odd frames, dot structure and flicker polaritiesof a display device according to Embodiment 15 of the invention.

FIGS. 33( a) and 33(b) are sectional view and plan view of a displaydevice according to Embodiment 16 of the invention.

FIG. 34 is an expanded sectional view showing the structure around aswitching element of a display device according to Embodiment 16 of theinvention.

FIG. 35( a) is a plan view showing a 4×4 dot section of pixels and FIGS.35( b) and 35(c) are schematic diagrams showing writing polarities tothe pixels of a display device according to Embodiment 16 of theinvention.

FIGS. 36( a) and 36(b) show light transmittance properties of a pixelportion in a display device according to Embodiment 16 of the invention.

FIGS. 37( a) and 37(b) are sectional view and plan view of a displaydevice according to Embodiment 17 of the invention.

FIG. 38 is an expanded sectional view showing the structure around aswitching element of a display device according to Embodiment 17 of theinvention.

FIG. 39( a) is a plan view showing a 4×4 dot section of pixels of adisplay device according to Embodiment 17 of the invention, and FIG. 39(b) is a schematic diagram showing the waveform applied to each of thepixels.

FIGS. 40( a) and 40(b) show light transmittance properties of a pixelportion in a display device according to Embodiment 17 of the invention.

FIG. 41 is a plan view showing a display device according to Embodiment18 of the invention.

FIG. 42 is a plan view showing another display device according toEmbodiment 18 of the invention.

FIGS. 43( a) and 43(b) show operation of a display device according toanother embodiment of the invention.

FIGS. 44( a), 44(b), 44(c) and 44(d) illustrate a first factor causingflicker.

FIGS. 45( a) and 45(b), and FIGS. 46( a) and (b) illustrate a secondfactor causing flicker.

FIG. 47 is a plan view showing a prior art display device.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described below withreference to the drawings.

Embodiment 1

FIG. 1 is a plan view showing a structure of one dot serving as aminimal display unit of an array substrate in a display device accordingto Embodiment 1 of the invention. FIGS. 2( a), 2(b) and 2(c) aresectional views of FIG. 1 taken along the lines A-A′, B-B′ and C-C′,respectively. In FIG. 1, gate wirings 4 feeding scanning signals andsource wirings 7 feeding image signals are arranged so as to intersectat approximately right angles. Nearby each intersection of the gatewiring 4 and the source wiring 7, a thin-film transistor (TFT) 5 isformed as a switching element. The TFT 5 formed on the gate wiring 4with an insulating layer in between comprises a semiconductor layer 8made of amorphous silicon. On the two sides of the semiconductor layer8, a projecting part of the source wiring 7 and a drain electrode 6 arearranged facing each other.

To the source wiring 7, a pixel electrode 1 is connected via the drainelectrode 6 of the TFT 5. An opposing electrode 2 functioning as astandard potential is arranged so as to face the pixel electrode 1. Theopposing electrode 2 is disposed between the two gate wirings 4, 4 in aparallel manner, and electrically connected to a common wiring 3 whichsupplies a prescribed electric potential (opposing voltage) to theopposing electrode 2.

The pixel electrode 1 comprises a first pixel electrode 1 a made of atransparent electric conductor disposed in the upper half of the dot anda second pixel electrode 1 b made of a metal material disposed in thelower half of the dot. The opposing electrode 2 comprises a firstopposing electrode 2 a made of a metal material which is disposed in theupper half of the dot so as to face the first pixel electrode 1 a and asecond opposing electrode 2 b made of a transparent electric conductordisposed in the lower half of the dot so as to face the second pixelelectrode 1 b.

On the gate wiring 4, a storage capacitor region 10 connected to thefirst pixel electrode 1 a is formed with an insulating layer in between.

As shown in FIGS. 1, 2(a), 2(b) and 2(c), on an array substrate 9, thegate wiring 4 the first opposing electrode 2 a and a common wiring 3 aare formed out of a first metal layer (ex. a three-layered structurecomprising titanium, aluminum and titanium). There upon, with aninsulating layer 11 a in between, the source wiring 7, the drainelectrode 6 and the second pixel electrode 1 b are formed out of asecond metal layer (ex. a three-layered structure comprising titanium,aluminum and titanium). There upon, with an insulating layer 11 b inbetween, the first pixel electrode 1 a and the second opposing electrode2 b are formed out of a transparent electric conductor layer (ex.Indium-Tin-Oxide (ITO)). The semiconductor layer 8 is formed between thefirst metal layer and the second metal layer and subjected topatterning. Both of the metal layers can be a uniform layer instead of amultilayer. For example, they can be formed of chromium, aluminum,tantalum or the like. It is also possible to use an alloy of molybdenumand tungsten, an alloy of molybdenum and tantalum or like alloys.

Particularly, using silver alloys (ex. an alloy of silver, palladium andcopper) is advantageous in that it lowers the wiring resistance andsimplifies the manufacturing process. Tin oxide and like oxides, organicconductive films as well as ITO can be used for forming the transparentelectric conductor layer.

The first pixel electrode 1 a and the second pixel electrode 1 b areconnected to each other through a contact hole 13 formed in theinsulating layer 11 b. The first opposing electrode 2 a is connected tothe common wiring 3 formed on the same layer, and the second opposingelectrode 2 b is connected to a common wiring through a contact hole 14formed in the insulating layers 11 a, 11 b. The number of contact holesand layer transformations (connections between different layers) areadjusted based on the shape and the number of electrodes.

Between the array substrate 9 and the opposing substrate (not shown)structured as described above, liquid crystal (not shown) is sealed in.Thus, a display device can be obtained.

The operation of the display device is described below. When anon-status voltage is applied to the gate wiring 4, a channel is formedon the semiconductor layer 8 and the gap between the source wiring 7 andthe drain electrode 6 becomes conductive. Then, the drain electrode 6and the pixel electrode 1 are charged to have the same electricpotential as that of the source wiring 7. Thereby, a difference appearsbetween the voltage fed to the pixel electrode 1 and that of theopposing electrode 2, to which a standard electric potential is applied.This generates electric fields substantially parallel to the substratesbetween the first pixel electrode 1 a and the first opposing electrode 2a and between the second pixel electrode 1 b and the second opposingelectrode 2 b and applied to the liquid crystal held between each of theelectrodes.

When an off-status voltage is applied to the gate wiring 4, channelformation is not achieved in the semiconductor layer 8, and thereforethere is no electrical continuity between the source wiring 7 and thedrain electrode 6 and the electric charges charged in the drainelectrode 6 and the pixel electrode 1 are retained. A storage capacitorelectrode 10 forms a storage capacitor region between the gate wiring 4and stabilizes the operation of the display device by compensating foror alleviating the potential difference due to leakage of electriccharge from the pixel electrode 1. Operation observed in one dot isexplained above. In a display device as a whole, a prescribed electricpotential is sent to each of the dots arranged in a matrix whilescanning the gate wirings one by one and applying to the source wiring asignal voltage appropriate to the dot scanned.

Operation of a display device according to the present embodiment willbe described below in more detail with reference to FIGS. 3 and 4. Thestructure shown in FIGS. 3 and 4 is the same as that shown in FIG. 2,and therefore the reference symbols used in FIG. 2 are omitted in FIGS.3 and 4 unless needed for explanation.

The signal voltage of each dot alternates in every frame in a mannersuch that the electric potential of the pixel electrode 1 assumes apositive or negative value relative to the opposing electrode 2. FIG. 3shows the condition where the gate voltage is at the off-level (Vg(OFF))after creating a positive electric potential in the pixel electrode 1 inthe first frame. FIG. 4 shows the condition where the gate voltage is atthe off-level after recording a negative electric potential into thepixel electrode in the second frame. The display device, while the firstand the second frames are being alternately repeated, is driven by thealternating current drive method. To simplify the explanation, theelectric potential of the opposing electrode 2 is made a constant groundpotential; however, if modulation in accordance with the polarity of thepixel electric potential is added to the opposing voltage and the gatevoltage, the amplitude of the signal voltage can be reduced.

As shown in FIG. 3, in the first frame, the first pixel electrode 1 aand the second pixel electrode 1 b have a positive electric potentialand the first opposing electrode 2 a and the second opposing electrode 2b have a ground potential, generating an electric field as shown by thearrows in the figure. Therefore, in the upper half of the dot, anelectric field is generated from the transparent first pixel electrode 1a to the opaque first opposing electrode 2 a and the transparentelectrode (the shadowed portion of the figure) has a relatively positiveelectric potential; however, in the lower half of the dot, an electricfield is generated from the opaque second pixel electrode 1 b to thetransparent second opposing electrode 2 b and the transparent electrode(shadowed portion of the figure) has a relatively negative electricpotential.

On the other hand, as shown in FIG. 4, in the second frame, the firstpixel electrode 1 a and the second pixel electrode 1 b have a negativeelectric potential and the first opposing electrode 2 a and the secondopposing electrode 2 b have a ground potential, generating an electricfield as shown by the arrows in the figure. Therefore, in the upper halfof the dot, an electric field is generated from the opaque firstopposing electrode 2 a to the transparent first pixel electrode 1 a andthe transparent electrode (shadowed portion of the figure) has arelatively negative electric potential; however, in the lower half ofthe dot, an electric field is generated from the transparent secondopposing electrode 2 b to the opaque second pixel electrode 1 b and thetransparent electrode (shadowed portion of the figure) has a relativelypositive electric potential.

The light passing through spaces or transparent electrodes (shadowedportion of the figure) in a dot, becomes brighter in portions where,among the pixel electrode 1 and the opposing electrode 2, thetransparent electrode has a negative electric potential relative to theopaque electrode compared to portions where the transparent electrodehas a positive electric potential relative to the opaque electrode.Therefore, in the first frame shown in FIG. 3, the lower half of the dotis brighter and, in the second frame shown in FIG. 4, the upper half ofthe dot becomes brighter. As described above, either the upper half orthe lower half of the dot alternately becomes brighter, and thereforethe contrast within a dot is canceled from frame to frame and theflicker phenomenon does not occur.

In the present embodiment, since the partition line which divides thedot into the upper and lower portions exists on the common wiring 3, tworegions having opposite flicker polarities (light or dark polarity) canbe formed in a single display unit without an additional electrode layeror switching element. Therefore, the embodiment has the advantage thatflicker can be reduced or eliminated without increased production costscaused by a more complicated manufacturing process or lowered apertureratio due to formation of a switching element.

In addition, the layer transformation and the material transformation(connections between different layers and materials) of the first andsecond pixel electrodes 1 a, 1 b and the first and second opposingelectrodes 2 a, 2 b occur above the common wiring 3, and therefore thereis no need to form contact holes 13, 14 in the aperture portion of thedisplay region to make the connections, improving the aperture ratio.Furthermore, in the structure where the common wiring 3 is disposed nearthe center of the display unit as in the present embodiment, if theconnections between the electrode materials are made above the commonwiring 3, the areas of the two regions having different flickerpolarities can be made almost equal, and a great reduction of flickercan be achieved by a simple structure. Generally speaking, theabove-mentioned improvement in the aperture ratio can be achieved if theconnections between the electrode materials are made above the commonwiring or the gate wiring.

Embodiment 2

FIG. 5 is a plan view showing the structure of one dot serving as aminimal display unit of an array substrate in a display device accordingto Embodiment 2 of the invention and FIGS. 6( a) 6(b); 6(c) and 6(d) aresectional views of FIG. 5 taken along the lines D-D′, E-E′, F-F′ andG-G′. In FIG. 5 and FIGS. 6( a), 6(b), 6(c) and 6(d), those elementswhich are identical to the elements of Embodiment 1 shown in FIGS. 1,2(a), 2(b), and 2(c) are identified with the same numerical symbols, andrepetitious explanation will be omitted.

A display device of the present embodiment is different from that ofEmbodiment 1 in that a storage capacitor electrode 10 is formed on thecommon wiring 3 instead of on the gate wiring 4 and a storage capacitorregion is formed between the common wiring 3 and the storage capacitorelectrode 10. This arrangement makes it possible to eliminate anadditional capacitor above the gate wiring 4 and achieve an uniformdisplay with a reduced distortion of the scanning voltage even on a widescreen. The principle used to eliminate flicker is the same as that usedin Embodiment 1.

In Embodiment 1, the storage capacitor electrode 10 is formed out of thesecond metal layer in the same layer as the source wiring 7, the drainelectrode 6 and the second pixel electrode 1 b and is connected to thesecond pixel electrode 1 b. Via the contact hole 13, the storagecapacitor electrode 10 is also connected to the first pixel electrode 1a which is formed out of a transparent electric conductor layer with aninsulating layer 11 b in between.

Therefore, as Embodiment 1, the structure of the present embodiment hasthe following advantages. By dividing the region (dot) constitutingdisplay unit into upper and lower portions and connections between thedifferent materials (material transformation) of the pixel electrode 1and the opposing electrode 2 on the common wiring 3 corresponding to thepartition line, it is possible to reduce or eliminate flicker withoutsuffering from increased production costs caused by a more complicatedmanufacturing process or a lowered aperture ratio attributable to theformation of a switching element. Furthermore, since connections betweenthe electrode materials are made above the wiring, formation of acontact hole in the aperture of the display region for makingconnections between different materials becomes unnecessary, and thisenhances the aperture ratio.

In the following embodiments, the storage capacitor electrode is formedon the common wiring 3 as in the present embodiment; however, it can beformed on the gate wiring 4 as in Embodiment 1.

Embodiment 3

FIG. 7 is a plan view showing the structure of one dot serving as aminimal display unit of an array substrate in a display device accordingto Embodiment 3 of the invention. In FIG. 7, those elements which areidentical to the elements of Embodiment 1 shown in FIG. 1 are identifiedwith the same numerical symbols, and repetitious explanation will beomitted.

In the display device of the present embodiment, the region 81corresponding to the black matrix formed as an opaque layer on theopposing substrate (not shown) facing the array substrate shown in FIG.1 is indicated by the region outlined with broken lines and filled byoblique lines. In other words, the region 81 is an area where passinglight is blocked, and an aperture is formed in the center of the dot.

The outline of the region 81 runs along the middle of the first opposingelectrode 2 a and the second opposing electrode 2 b in the longitudinaldirection and makes the areas of the transparent electrode disposed inthe apertures in the upper and lower halves of a dot (i.e. the firstpixel electrode 1 a and the second opposing electrode 2 b) equal. As aresult, it is possible to reliably cancel the flicker polarities in adot. This structure is particularly useful when the actual areas of thetransparent electrode differ in the upper and lower halves of a dot. Inthe present embodiment, the areas of the transparent electrode in theapertures in the upper and lower halves of a dot are made equal using ablack matrix; however, it is also possible to make the areas of thetransparent electrode equal by varying the width of the electrode andadjusting the length of the electrode. The black matrix can be formed onthe array substrate side. Furthermore, it is also possible to use ametal layer instead of the black matrix and make it function as anopaque layer by overlaying it on a part of the transparent electrodelayer. By forming an opaque layer such as a black matrix or the like onthe array substrate side, the effect of any misalignment of the twosubstrates is eliminated and the accuracy of the position of the opaquelayer with respect to the electrode is enhanced. This enhances theability to eliminate flicker. More preferably, flicker can be reliablyprevented by utilizing the results of experiments or simulations andadjusting the width of the opaque layer and electrode and the length ofthe electrode in a manner such that the effective areas of thetransparent electrode affecting the transmittance in the upper and lowerhalves of a dot becomes equal. This arrangement can be employed not onlyin a display device of Embodiment 1 but also in display devices of otherembodiments.

Embodiment 4

FIG. 8 is a plan view showing the structure of one dot serving as aminimal display unit of an array substrate in a display device accordingto Embodiment 4 of the invention. FIGS. 9( a) and 9(b) are sectionalviews of FIG. 8 taken along the lines H-H′ and I-I′. In FIGS. 8, 9(a)and 9(b), those elements which are identical to the elements ofEmbodiment 1 shown in FIGS. 1, 2(a), 2(b), and 2(c) are identified withthe same numerical symbols, and repetitious explanation will be omitted.

A display device according to the present embodiment is designed so thatthe inside of a dot is divided into right and left halves and flicker iscanceled between the two (left and right) regions.

The right region comprises a first pixel electrode 1 a made of atransparent electric conductor and a first opposing electrode 2 a madeof a metal material. The left region comprises a second pixel electrode1 b made of a metal material and a second opposing electrode 2 b made ofa transparent electric conductor. In the center of the dot, with theboundary line of the left and right regions in between, a first centralopposing electrode 2 c made of a metal material is formed on the rightside and a second central opposing electrode 2 d made of a transparentelectric conductor is formed on the left side. A common wiring 3 isdisposed above the center of the dot.

As shown in FIGS. 8, 9(a) and 9(b), on an array substrate 9, a gatewiring 4 the first opposing electrode 2 a, the common wiring 3 and thefirst central opposing electrode 2 c are formed out of a first metallayer. There upon, with an insulating layer 11 a in between, a sourcewiring 7, a drain electrode 6, the second pixel electrode 1 b and astorage capacitor electrode 10 are formed out of a second metal layer.Above the second metal layer, with an insulating layer 11 b in between,the first pixel electrode 1 a, the second opposing electrode 2 b and thesecond central opposing electrode 2 d are formed out of a transparentelectric conductor layer. The first pixel electrode 1 a is connected tothe storage capacitor electrode 10 through a contact hole 13, and thesecond opposing electrode 2 b and the second central opposing electrode2 d are connected to the common wiring 3 through a contact hole 14.

The display device having the above structure is advantageous in that itprevents flicker and readily obtains high definition images owing to areduced number of contact holes. Furthermore, it can enhance themanufacturing yield since the ratio of defects caused by poor contactbetween the constituent elements is lowered. The common wiring 3 canalso be disposed below the center of the dot.

Embodiment 5

FIG. 10 is a plan view showing the structure of one dot serving as aminimal display unit of an array substrate in a display device accordingto Embodiment 5 of the invention. FIGS. 11( a) and 11(b) are sectionalviews of FIG. 10 taken along the lines J-J′ and K-K′. In FIGS. 10, 11(a)and 11(b), those elements which are identical to the elements ofEmbodiment 1 shown in FIGS. 1, 2(a), 2(b), and 2(c) are identified withthe same numerical symbols, and repetitious explanation will be omitted.

In FIG. 10, the region 41, whose outline is shown by the broken line,indicates a region of one dot.

In the present embodiment, the dot is divided into two subdots SD1 andSD2 having opposite flicker polarities (light or dark polarity) and theflicker polarities are canceled within the dot.

The two subdots SD1 and SD2 are formed by dividing the dot into left andright portions with the center at a source wiring 7. The portionsreceive signals from the same gate wiring 4 and source wiring 7. Theright subdot SD1 comprises a first pixel electrode 1 a made of atransparent electric conductor and a first opposing electrode 2 a madeof a metal material. In contrast to SD1, the left subdot SD2 comprises asecond pixel electrode 1 b made of a metal material and a secondopposing electrode 2 b made of a transparent electric conductor. Thefirst pixel electrode 1 a and the second pixel electrode 1 b areconnected to the same source wiring 7 through TFTs 42, 43, respectively.Storage capacitor electrodes 10 b, 10 c are formed on a common wiring 3and connected to the first pixel electrode 1 a and the second pixelelectrode 1 b, respectively.

As shown in FIGS. 10, 11(a) and 11(b), on an array substrate 9, the gatewiring 4, the first opposing electrode 2 a and the common wiring 3 areformed out of a first metal layer. There upon, with an insulating layer11 a in between, the source wiring 7, drain electrodes 6 a, 6 b, thesecond pixel electrode 1 b and the storage capacitor electrodes 10 b, 10c are formed out of a second metal layer. There upon, with an insulatinglayer 11 b in between, the first pixel electrode 1 a and the secondopposing electrode 2 b are formed out of a transparent electricconductor layer. The first pixel electrode 1 a is connected to thestorage capacitor electrode 10 b through the contact hole 13, and thesecond opposing electrode 2 b is connected to the common wiring 3through the contact hole 14.

This structure achieves a display which is free from flicker, since thedifference in brightness attributable to the flexoelectric effect or aperipheral electric potential is offset between the left and rightsubdots.

In the display device of the present embodiment, each dot is dividedinto two subdots SD1 and SD2, and the TFTs 42, 43 are provided in thesubdots SD1 and SD2, respectively. Therefore, even when a defect arisesin one of the TFTs 42, 43, the subdot having the other TFT operatesnormally. Therefore, the display device has the advantage that there isa low possibility of having a non-lighting dot caused by an entire dotbeing defective.

Furthermore, the two subdots SD1 and SD2 are arranged so as to hold thesource wiring 7 in between. Since both subdots SD1 and SD2 use the samesource wiring 7, there is no need to increase the number of sourcewirings 7.

As shown in FIG. 10, the electrodes 1 a and 2 b extend upward anddownward from the contact holes 13, 14. Therefore, the number of contactholes can be reduced in the present embodiment compared to the structurein Embodiments 1 and 2 in which the electrodes extend in only onedirection from the contact holes. This makes it possible to readilyprovide high definition images and enhance the manufacturing yield sincethe probability of a defect caused by poor contact between theconstituent elements is lowered.

In order to further enhance the flicker reducing effect, bringing theflicker polarities of the two dots into balance is desirable. For thatpurpose, it is desirable that the capacities of the two storagecapacitor electrodes 10 b, 10 c be made equal and it is advantageousthat the two storage capacitor electrodes 10 b, 10 c be designed to beformed of the same material, thereby making the areas of the two storagecapacitor electrodes equal. For that purpose, in the right subdot SD1 ofthe present embodiment, the transparent first pixel electrode 1 a makesa connection between layers and the storage capacitor electrode 10 b ismade out of a metal layer. As a result, the design period of the TFTarray is shortened without adversely affecting the design, enhancing themanufacturing yield by using a design having a high tolerance for theerrors introduced by the manufacturing process.

Next, examples of the repeated patterns of dots in the entire arraysubstrate and desirable combinations with driving methods will beexplained. FIGS. 12( a) and 12(b) show repeated patterns of the subdotsSD1 and SD2 shown in FIG. 10, wherein the left subdot SD2 (the pixelelectrode is made out of a metal layer) is defined as P and the rightsubdot SD1 (the pixel electrode is made out of a transparent electrodelayer) is defined as Q. As shown in FIG. 10, between each pair of dots,there is either a first opposing electrode 2 a or a second opposingelectrode 2 b. With respect to the pattern design, the structure inwhich the left and right dots share the first opposing electrode 2 a orthe second opposing electrode 2 b is preferable to enhance the apertureratio. Therefore, in the dot array arranged along the gate wiring 4, onthe right side of a dot having the two subdots arranged in the order ofPQ, it is preferable to place a dot having the two subdots arranged inthe order of QP. In other words, for any two horizontally adjacent dots,it is preferable that the arrangement of the subdots thereof bereversed.

On the other hand, regarding vertically adjacent dots, it is preferablethat the arrangement cycle of the subdots differ from the inversioncycle of the driving voltages. If the two cycles are coincident witheach other, the effect of inversion is offset and vertical lines mayarise because dots having the same flicker polarity are arranged alongthe source wiring 7.

Desirable subdot patterns are explained below with reference to concreteexamples. Regarding the subdot arrangement of vertically adjacent dots,the following two patterns are better suited for practical use in viewof the layout design. In the first pattern, as shown in FIG. 12( a), thearrangement of the right and left subdots is reversed between any twovertically adjacent dots, and in the other, as shown in FIG. 12( b), thearrangement of the right and left subdots is kept the same withoutreversing.

FIGS. 13( a) to 13(f) illustrate conditions in which the polarities ofthe voltage applied to each dot are inverted between the two frames,showing several polarity driving voltage inversion methods. Among thefigures, FIG. 13( a) shows the frame-inversion drive method and FIG. 13(b) shows the column-inversion drive method. In both methods, a voltageis applied in such a manner that dots aligned in the vertical directionhave the same polarity. It is desirable that these driving methods beused with the subdot arrangement pattern shown in FIG. 12( a). This isbecause, in vertically adjacent rows, subdot arrays are inverted and thepolarity of the voltage applied to the pixel electrodes is the same,making flicker more indistinctive as subdots having the same flickerpolarities are not continuously aligned in the vertical direction.

Among the polarity inversion methods shown in FIGS. 13( a) to 13(f), itis preferable that the line-inversion drive method (row-inversion drivemethod) shown in FIG. 13( c) and the dot-inversion drive method shown inFIG. 13( d) be used with the subdot arrangement pattern shown in FIG.12( b). This is because, in vertically adjacent rows, subdot arrays havethe same polarity pattern and the polarity of the voltage applied to thepixel electrodes is inverted, making flicker more indistinctive assubdots having the same flicker polarities are not continuously alignedin the vertical direction.

In the polarity inversion methods used to drive the liquid crystal,there are several ways in which inversion is performed every n linesinstead of every line as shown in FIGS. 13( c) and 13(d). The two-lineinversion drive method shown in FIG. 13( e) (inversion is performedevery two lines) and the two-line-dot inversion drive method shown inFIG. 13( f) are the examples of the case when n is 2. When inversiondrive is performed every n lines, a display free from severe problems invisibility can be achieved if the subdot array is inverted every n linesand the array cycle differs from the inversion cycle of the drivingvoltage.

When combined with the subdot arrangement shown in FIG. 12( a), theflicker polarities of vertically adjacent subdots are repeatedlyinverted for n lines and a portion appears every n lines wherevertically adjacent subdots have the same flicker polarities. On theother hand, when combined with the subdot arrangement shown in FIG. 12(b), vertically adjacent subdots have the same flicker polarities for nlines and a portion appears every n lines where the flicker polaritiesof vertically adjacent subdots are inverted. Therefore, when n is 2, andeither the subdot arrangement shown in FIG. 12( a) or that of 12(b) isadopted, two lines of subdots having the same flicker polarities arecontinuously arranged in the vertical direction and then inverted,obtaining a desirable display. When n is 3 or greater, combination withthe subdot arrangement shown in FIG. 12( a) results in an increasednumber of inversions of flicker polarity, and is thus desirable.

Embodiment 6

FIG. 14 is a plan view showing the structure of one dot serving as aminimal display unit of an array substrate in a display device accordingto Embodiment 6 of the invention and FIGS. 15( a), 15(b), 15(c) and15(d) are sectional views of FIG. 14 taken along the lines L-L′, M-M′,N-N′ and O-O′. The present embodiment is a combination of Embodiments 2and 5, and therefore those elements which are identical to the elementsof Embodiments 2 and 5 are identified with the same numerical symbols,and repetitious explanation will be omitted.

In a display device of the present embodiment, the dot 51, whose outlineis shown by the broken line in FIG. 14, is divided into two subdots SD3and SD4. The flicker polarities are canceled between the upper and lowerhalves of the subdots SD3 and SD4.

The two subdots SD3 and SD4 are formed by dividing the dot into left andright portions with the center at a source wiring 7. The portionsreceive signals from the same gate wiring 4 and source wiring 7. Theupper portions of the right subdot SD3 and the left subdot SD4 comprisea first pixel electrode 1 a made of a transparent electric conductor anda first opposing electrode 2 a made of a metal material. The lowerportions of the right subdot SD3 and the left subdot SD4 subdot comprisea second pixel electrode 1 b made of a metal material and a secondopposing electrode 2 b made of a transparent electric conductor. Thesecond pixel electrodes 1 b in the subdots SD3 and SD4 are connected tothe same source wiring 7 through TFTs 42, 43, respectively. Storagecapacitor electrodes 10 are formed on the common wiring 3 in the subdotsSD3 and SD4 and connected to the first pixel electrode 1 a and thesecond pixel electrode 1 b, respectively.

As shown in FIGS. 14, 15(a), 15(b), 15(c) and 15(d) on an arraysubstrate 9, the gate wiring 4, the first opposing electrode 2 a and thecommon wiring 3 are formed out of a first metal layer. There upon, withan insulating layer 11 a in between, the source wiring 7, drainelectrodes 6 a, 6 b, the second pixel electrode 1 b and the storagecapacitor electrode 10 are formed out of a second metal layer. Thereupon, with an insulating layer 11 b in between, the first pixelelectrode 1 a and the second opposing electrode 2 b are formed out of atransparent electric conductor layer. The first pixel electrode 1 a isconnected to the storage capacitor electrode 10 through the contact hole13, and the second opposing electrode 2 b is connected to the commonwiring 3 through the contact hole 14.

In the display device of the present embodiment, as in Embodiment 5,each dot is divided into two subdots SD3 and SD4, and the TFTs 42, 43are provided in the subdots SD3 and SD4, respectively. Therefore, evenwhen a defect arises in one of the TFTs 42, 43, the subdot having theother TFT operates normally. Therefore, the display device has theadvantage that there is a low possibility of having a non-lighting dotcaused by an entire dot being defective.

Furthermore, as in Embodiment 5, the two subdots SD3 and SD4 arearranged so as to hold the source wiring 7 in between. Since bothsubdots SD3 and SD4 use the same source wiring 7, there is no need toincrease the number of source wirings 7.

A distinctive advantage of the present embodiment is that it can obtainexcellent flicker polarities despite its driving method, since the twosubdots SD3 and SD4 are symmetrically shaped.

Embodiment 7

FIG. 16 is a plan view showing the structure of one dot serving as aminimal display unit of an array substrate in a display device accordingto Embodiment 7 of the invention and FIGS. 17( a), 17(b) and 17(c) aresectional views of FIG. 14 taken along the lines P-P′, Q-Q′ and R-R′. InFIGS. 16, 17(a), 17(b), 17(c) and 17(d), those elements which areidentical to the elements of Embodiment 1 shown in FIGS. 1, 2(a), 2(b),and 2(c) are identified with the same numerical symbols, and repetitiousexplanation will be omitted.

According to a display device of the present embodiment, a pixelelectrode 1 and an opposing electrode 2 are formed out of a metal layerand an intermediate electrode 61 made of a transparent conductive layeris formed between the two electrodes. The widths of the spaces betweenthe opposing electrode 2 and the intermediate electrode 61 and betweenthe intermediate electrode 61 and the pixel electrode 1 are madeapproximately equal. The pixel electrode 1, the intermediate electrode61 and the opposing electrode 2 are electrically connected to each otherby a resistor 62 having belt-shaped ends.

As shown in FIGS. 16, 17(a), 17(b) and 17(c), on an array substrate 9, agate wiring 4, the opposing electrode 2 and a common wiring 3 are formedout of a first metal layer. There upon, with an insulating layer 11 a inbetween, a source wiring 7, a drain electrode 6, the pixel electrode 1and a storage capacitor electrode 10 are formed out of a second metallayer. There upon, with an insulating layer 11 b in between, theintermediate electrode 61 is formed out of a transparent electricconductor layer. On the intermediate electrode 61, with an insulatinglayer 11 c in between, a resistor 62 is formed out of a metal-oxidelayer or a semiconductor layer. High-resistance ITO, tin oxide or thelike can be used to obtain a metal-oxide layer. An example of asemiconductor layer include an amorphous silicon layer.

The pixel electrode 1 is connected to the resistor 62 through a contacthole 67 formed in the insulating layers 11 b, 11 c. The opposingelectrode 2 is connected to the resistor 62 through a contact hole 68formed in the insulating layers 11 a, 11 b, 11 c. The intermediateelectrode 61 is connected to the resistor 62 through a contact hole 69formed in the insulating layer 11 c.

FIG. 18 is an equivalent circuit diagram of the array substratedescribed above. In this figure, the opposing electrode 2 is assumed tohave a ground potential through the common wiring 3 and a signalelectric potential (Va) applied to the pixel electrode 1 is assumed tobe positive. In this case, by making the resistances of each resistor 62approximately the same, the electric potential of the intermediateelectrode 61 becomes the average value (Va/2) of the electric potentialsof the pixel electrode 1 and the opposing electrode 2.

In FIG. 16, the distances between the opposing electrode 2 and theintermediate electrode 61 and between the intermediate electrode 61 andthe pixel electrode 1 are assumed to be substantially the same, andtherefore the strengths of the electric fields generated in spaces S1,S2, S3 and S4 which are formed between the electrodes become the sameand their directions are as shown by the arrows in the figure. In thiscase, in the left intermediate electrode 61, the left half serves as apositive electrode relative to space S1 and the right half serves as anegative electrode relative to space S2. On the other hand, in the rightintermediate electrode 61, the left half serves as a negative electroderelative to space S3 and the right half serves as a positive electroderelative to space S4. Therefore, between the left side and the rightside of the intermediate electrode 61 made of a transparent electricconductor, differences in brightness caused by the flexoelectric effector a peripheral electric potential can be cancelled.

When a negative signal voltage is applied to the next frame, thedirections of the electric fields and operations of each space servingas a positive or a negative electrode are reversed; however, asexplained above, differences in brightness can be cancelled between theright and the left sides of the intermediate electrode 61. Therefore,the brightness of the positive and the negative frames becomes the samein the dot as a whole, eliminating flicker.

The intermediate electrode 61 is resistively connected to the electrodesto which an electric potential is applied (the pixel electrode 1 and theopposing electrode 2), and therefore its electric potential is stablewithout floating. This makes it possible to display stable images.

In the present embodiment, the intermediate electrode 61 is resistivelyconnected to the pixel electrode 1 and the opposing electrode 2;however, it can also be arranged so that an external electric potentialis applied to the intermediate electrode 61 to stabilize the electricpotential of the intermediate electrode 61.

In the present embodiment, the intermediate electrode 61 is made of atransparent electric conductor and the pixel electrode 1 and theopposing electrode 2 are formed out of a metal layer; however, by makinga connection between layers by forming a contact hole, etc., it is alsopossible to form the pixel electrode 1 and the opposing electrode 2 of atransparent electric conductor and the intermediate electrode 61 out ofa metal layer. This arrangement increases the number of electrodes madeof a transparent electric conductor, obtaining brighter images.

It is preferable that the electric potential of the intermediateelectrode 61 be the average of the electric potentials of the pixelelectrode 1 and the opposing electrode 2 as in the present embodiment;however, setting the electric potential of the intermediate electrode 61anywhere between those of the pixel electrode 1 and the electricpotential also achieves a flicker reduction.

According to the present embodiment, the resistor 62 is formed on theintermediate electrode 61 with the insulating layer 11 c in between;however, it is not necessary to protect the intermediate electrode 61 bythe insulating layer 11 c, if it is free from damage while the resistor62 is being subjected to patterning. Therefore, as shown in FIG. 17( d),it is also possible to form the portion taken along the line P-P′ inFIG. 16 without having the insulating layer 11 c. This allows areduction of the manufacturing processes and production costs.

In this case, a concrete example of a way to obtain the resistor 62 isas follows. A resin-based resistance-material layer is formed on theintermediate electrode 61 made of ITO and etched using a photoresisthaving a predetermined pattern. It is also possible to use aphotosensitive material as a resin material and directly conductpatterning by exposure to light. As another example, it is also possibleto apply a resistor to only a prescribed area by mask deposition.

Embodiment 8

FIG. 19 is a plan view showing the structure of one dot serving as aminimal display unit of an array substrate in a display device accordingto Embodiment 8 of the invention and FIGS. 20( a), 20(b) and 20(c) aresectional views of FIG. 19 taken along the lines S-S′, T-T′ and U-U′. Inthe present embodiment, instead of connecting the pixel electrode 1, theintermediate electrode 61 and the opposing electrode 2 by a resistiveelement, capacitive coupling is used. In other respects, theconstruction thereof is the same as that of Embodiment 5. Therefore, inthe present embodiment, those elements which are identical to theelements of Embodiment 5 are identified with the same numerical symbols,and repetitious explanation will be omitted.

As shown in FIG. 19, according to the present embodiment, extensions 71projecting into the left and the right sides from the top end of theintermediate electrode 61 are formed instead of forming the resistor 62shown in FIG. 16. By placing the extension 71 on top of the pixelelectrode 1 and the opposing electrode 2, coupling capacity regions 72a, 72 b are formed.

As shown in FIGS. 19 and 20( a), the extension 71 extending from theintermediate electrode 61 is formed on the insulating layer 11 b. Acoupling capacity region 72 a is formed between the extension 71 and thepixel electrode 1 with an insulating layer 11 a in between. A couplingcapacity region 72 b is formed between the extension 71 and the opposingelectrode 2 with the insulating layers 11 a, 11 b in between.

FIG. 21 shows an equivalent circuit of the array substrate describedabove. Like in Embodiment 7, it is assumed that the opposing electrode 2has a ground potential through the common wiring 3 and that a positivesignal electric potential (Va) is applied to the pixel electrode 1. Inthis case, by making the capacitances of the coupling capacity regions72 a, 72 b approximately equal, the electric potential of theintermediate electrode 61 becomes the average value (Va/2) of theelectric potentials of the pixel electrode 1 and the opposing electrode2.

Like in Embodiment 7, In FIG. 19, the distances between the opposingelectrode 2 and the intermediate electrode 61 and between theintermediate electrode 61 and the pixel electrode 1 are assumed to besubstantially the same, and therefore the strengths of the electricfields generated in spaces S1, S2, S3 and S4 formed between theelectrodes become the same and their directions are as shown by thearrows in the figure. Therefore, as in Embodiment 7, between the leftside and the right side of the intermediate electrode 61 made of atransparent electric conductor, differences in brightness caused by theflexoelectric effect or a peripheral electric potential can becancelled.

When a negative signal voltage is applied to the next frame, thedirections of the electric fields and the operation of each spaceserving as a positive or a negative electrode are reversed; however, asexplained above, differences in brightness can be cancelled between theright and the left sides of the intermediate electrode 61. Therefore,the brightness of the positive and the negative frames become the samein the dot as a whole, eliminating flicker.

A display device according to the present embodiment can reduce fractiondefectives and production costs compared to that of Embodiment 7, sinceformation of a resistor and a coupling part (contact hole) connectingthe resistor to each electrode becomes unnecessary.

In the present embodiment, as in Embodiment 7, by making connectionswith different layers by forming a contact hole, etc., it is alsopossible to form the pixel electrode 1 and the opposing electrode 2 of atransparent electric conductor and the intermediate electrode 61 out ofa metal layer. This arrangement increases the number of electrodes madeof a transparent electric conductor, obtaining brighter images.

It is preferable that the electric potential of the intermediateelectrode 61 be the average of the electric potentials of the pixelelectrode 1 and the opposing electrode 2; however, setting the electricpotential of the intermediate electrode 61 anywhere between those of thepixel electrode 1 and the electric potential also achieves a flickerreduction.

Taking the difference in the thickness of the insulating layers in thecoupling capacity regions 72 a, 72 b into consideration, in order tomake the capacities of the coupling capacity regions 72 a, 72 b equal,it is preferable to adjust the opposing area of the electrodes in thecoupling capacity regions 72 a, 72 b. For example, this can be done byvarying the widths of the pixel electrode 1 and the opposing electrode 2in the portions where the coupling capacity regions 72 a, 72 b areformed.

In the present embodiment, two intermediate electrodes 61 are separatelyarranged; however, as shown in FIG. 22, it is also possible to connectthe two intermediate electrodes 61 by the extension 71. This arrangementreliably makes the electric potentials of the two intermediateelectrodes 61 equal. FIG. 20( d) shows the sectional view taken alongthe line S-S′ in FIG. 22. In this figure, the left and right couplingcapacity regions 72 b, 72 b are in parallel, and therefore it isdesirable that the total capacity of the two regions 72 b, 72 b be equalto that of the coupling capacity region 72 a. Specifically, this isachieved by varying the widths of the pixel electrode 1 and the opposingelectrode 2 as described above.

Embodiment 9

FIG. 23 is a plan view showing the structures of two adjacent dots on anarray substrate in a display device according to Embodiment 9 of theinvention. FIGS. 24( a), 24(b) and 24(c) are sectional views taken alongthe lines V-V′, W-W′ and X-X′ of FIG. 23.

In the display device according to Embodiment 5 shown in FIGS. 10, 11(a)and 11(b), flicker polarities are cancelled in a dot by dividing the dotinto two subdots and making the flicker polarities different in eachsubdot. On the other hand, in the display device according to thepresent embodiment, two adjacent dots D1 and D2 are structured so thatthe flicker polarities are cancelled between the dots when a signalvoltage having the same polarity is applied to the two dots D1 and D2.In FIGS. 23, 24(a), 24(b) and 24(c), those elements which are identicalto the elements of Embodiment 5 are identified with the same numericalsymbols, and repetitious explanation will be omitted.

As shown in FIG. 23, the left dot D1 comprises a first pixel electrode 1a and a first opposing electrode 2 a. The first pixel electrode 1 a ismade of a transparent electric conductor and the first opposingelectrode 2 a is formed out of a metal layer. The right dot D2 comprisesa second pixel electrode 1 b and a second opposing electrode 2 b. Thesecond pixel electrode 1 b is formed out of a metal layer and the secondopposing electrode 2 b is made of a transparent electric conductor. Thefirst pixel electrode 1 a and the second pixel electrode 1 b areconnected to separate source wirings 7 via separate TFTs 5. Thestructure of the TFT 5 of the present embodiment is the same as that ofEmbodiment 1. On a gate wiring 4, storage capacitor electrodes 10 d, 10e are formed and connected to the first pixel electrode 1 a and thesecond pixel electrode 1 b, respectively.

As shown in FIGS. 23, 24(a), 24(b) and 24(c), on an array substrate 9,the gate wiring 4, the first opposing electrode 2 a and a common wiring3 are formed out of a first metal layer. There upon, with an insulatinglayer 11 a in between, the source wiring 7, a drain electrode 6 and thesecond pixel electrode 1 b are formed out of a second metal layer. Thereupon, with an insulating layer 11 b in between, the first pixelelectrode 1 a, the second opposing electrode 2 b and the storagecapacitor electrodes 10 d, 10 e are formed of a transparent electricconductor layer. The first pixel electrode 1 a is connected to the drainelectrode 6 through a contact hole 13. The second opposing electrode 2 bis connected to the common wiring 3 through a contact hole 14.

In this structure, when a positive voltage is applied to dots D1 and D2,in the left dot D1, the transparent first pixel electrode 1 a has arelatively positive electric potential, and, in the right dot D2, thetransparent second opposing electrode 2 b has a relatively negativeelectric potential. When a negative voltage is applied to dots D1 andD2, in the left dot D1, the transparent first pixel electrode 1 a has arelatively negative electric potential, and, in the right dot D2, thetransparent second opposing electrode 2 b has a relatively positiveelectric potential. Thereby, the flicker polarities are cancelledbetween the two dots D1 and D2.

In the display device of the present embodiment, in order to furtherenhance the flicker reduction effect, bringing the flicker polarities ofthe two dots D1 and D2 into balance is desirable. For that purpose, itis desirable that the capacities of the two storage capacitor electrodes10 d, 10 e be made equal and it is advantageous that the two storagecapacitor electrodes 10 d, 10 e be designed to be formed out of the samematerial, thereby making the areas of the two storage capacitorelectrodes equal. In the right subdot SD2 of the present embodiment, asshown in FIG. 24( c), the transparent second pixel electrode 1 b makes aconnection between layers and the storage capacitor electrode 10 e ismade of a transparent electric conductor. As a result, the design periodof the TFT array is shortened without adversely affecting the design,enhancing the manufacturing yield by using a design having a hightolerance for the errors introduced by the manufacturing process. As inEmbodiment 5, storage capacitor electrodes 10 d, 10 e can also be formedon the gate wiring 4 out of a metal layer.

Embodiment 10

FIG. 25 is a plan view showing the structures of two adjacent dots on anarray substrate in a display device according to Embodiment 10 of theinvention. FIGS. 26( a), 26(b) and 26(c) are sectional views of FIG. 25taken along the lines AA-AA′, BB-BB′ and CC-CC′.

In the display device of Embodiment 9, the storage capacitor electrodes10 d, 10 e are formed on the gate wiring 4. On the other hand, in thedisplay device of the present embodiment, storage capacitor electrodes10 b, 10 c are formed on a common wiring 3. In FIGS. 25, 26(a), 26(b)and 26(c), those elements which are identical to the elements ofEmbodiment 9 are identified with the same numerical symbols, andrepetitious explanation will be omitted.

As shown in FIGS. 25, 26(a), 26(b) and 26(c), on an array substrate 9, agate wiring 4, a first opposing electrode 2 a and a common wiring 3 areformed out of a first metal layer. There upon, with an insulating layer11 a in between, a source wiring 7, a drain electrode 6, a second pixelelectrode 1 b and storage capacitor electrodes 10 b, 10 c are formed outof a second metal layer. There upon, with an insulating layer 11 b inbetween, a first pixel electrode 1 a and a second opposing electrode 2 bare formed of a transparent electric conductor layer. The first pixelelectrode 1 a is connected to the storage capacitor electrode 10 bthrough a contact hole 13. The second opposing electrode 2 b isconnected to the common wiring 3 through a contact hole 14.

Like that in Embodiment 9, in the display device of the presentembodiment, flicker polarities are cancelled between the two adjacentdots D1 and D2. The present embodiment has a distinctive feature in thatan uniform display with a reduced distortion of scanning voltage can beobtained even on a wide screen because its additional capacitance of thegate wiring 4 is reduced.

Like in Embodiment 9, in the display device of the present embodiment,in order to further enhance the flicker reduction effect, bringing theflicker polarities of the two dots D1, D2 into balance is desirable. Forthat purpose, it is desirable that the capacities of the two storagecapacitor electrodes 10 b, 10 c be made equal and it is advantageousthat the two storage capacitor electrodes 10 b, 10 c be designed to beformed of the same material, thereby making the areas of the two storagecapacitor electrodes equal. In the left D1 of the present embodiment,the transparent first pixel electrode 1 a makes a connection betweenlayers and the storage capacitor electrode 10 b is formed out of a metallayer. As a result, the design period of the TFT array is shortenedwithout adversely affecting the design, enhancing the manufacturingyield by using a design having a high tolerance for the errorsintroduced by the manufacturing process. Like in Embodiment 9, thestorage capacitor electrodes 10 b, 10 c can also be formed on the commonwiring 3 out of a transparent electric conductor layer.

Embodiment 11

The present embodiment relates to color display devices with structuresas describe in the above embodiments of the present invention. In acolor display device having dots arranged in a matrix, a black matrixand a color filter are generally formed in an opposing substrate facingan array substrate. The color filter is formed on an aperture of theblack matrix, and each pixel thereof has a color layer of red, green orblue so that, in the display device as a whole, these three colors arerepeated in an array. In other words, as shown in the area enclosed bythe bold line in FIG. 27, it is common that one pixel 91 is formed outof three dots each having one of three primary colors, i.e, red (R),green (G) and blue (B).

As shown in FIG. 28, this color display device comprises a scanningsignal driver M1 supplying a scanning signal by applying a prescribedvoltage to a gate wiring 4 and an image signal driver M2 supplying animage signal by applying a prescribed voltage to a source wiring 7.These drivers M1, M2 are controlled by a controller C. In the colordisplay device having such structure, a bright image with a wide viewingangle and reduced flicker can be obtained by arranging each dot shown inFIG. 27 so as to have a structure as described in the above embodimentsof the invention.

Embodiment 12

The present embodiment relates to a color display device in which, inthe dot array on an array substrate shown in FIG. 27, three dots (RGB)in one pixel are structured so as to have the same structure and flickerpolarities are cancelled between any two adjacent pixels. FIG. 29 showsdot arrays in the two adjacent pixels.

In FIG. 29, dots P and Q are structured so that they have flickerpolarities opposite of each other relative to the same drive voltage.For example, the structure of dot D1 in Embodiments 9 and 10 correspondsto that of P and the structure of dot D2 corresponds to that of Q. Thesubscripts R, G and B express the colors of each dot. According to thepresent embodiment, as shown in the figure, in the two adjacent pixels91, 91, the structure of the dots is the same within a pixel anddifferent from that of the dots in the adjacent pixel. This makes itpossible to readily cancel flicker polarities between any two adjacentpixels. Furthermore, since the dots within a pixel have the sameproperties, this arrangement has an advantage that color distortion canbe prevented even in halftone display which tends to be adverselyaffected by the difference between the brightness and voltageproperties.

Embodiment 13

In the color display device of Embodiment 12, the dots have the samestructure within a pixel. On the other hand, as shown in FIG. 30, in acolor display device according to the present embodiment, any twoadjacent dots are arranged so as to have different structures. Thereby,flicker polarities can be cancelled between more subdivided regions.

Embodiment 14

The present embodiment relates to a color display device having the dotarray as shown in FIG. 29 which employs a drive method further enhancingthe flicker reduction effect.

In order to reduce flicker, it is preferable that the arrangement cycleof the regions showing the same flicker polarity relative to a samevoltage differ from the inversion cycle of a driving voltage. If the twocycles are coincident with each other, the effect of inversion isoffset, adversely affecting the flicker reduction effect.

Next, examples of the repeated patterns of dots (array of P and Q inFIG. 29) and desirable combinations with the inversion methods of adrive voltage will be explained. FIGS. 31( a) to 31(f) show, when it isassumed, as shown in FIG. 29, that the dots within a pixel 91 have thesame structure as in, the polarities of the drive wave in an odd frame,the dot structure and the patterns of flicker polarity (odd frame)defined by their combination. Although not shown in the figures, an evenframe has a pattern of drive wave polarity inverted from that of an oddframe, resulting in a pattern of flicker polarity opposite to that of anodd frame.

An enhanced flicker reduction effect can be obtained in an arrangementin which the distribution of flicker polarity of pixels or dots isinverted every line.

Specific examples of such combinations are as follows:

FIG. 31( a): Combination of a line-inversion (row-inversion) drive and aline-non-inversion (row-non-inversion) dot array;

FIG. 31( c): Combination of a frame-inversion drive and a line-inversion(row-inversion) dot array; and

FIG. 31( e): Combination of a column-inversion drive and aline-inversion (row-inversion) dot array.

On the other hand, for example, when a checkerboard pattern appears on acomputer screen as wallpaper, etc., it is preferable that, between thepixels or dots, flicker polarity be inverted every two lines to preventinterference between the checkerboard pattern and the flicker pattern.Specific examples of such combinations are as follows:

FIG. 31( b): Combination of a line-inversion (row-inversion) drive and atwo-line-inversion (two-row-inversion) dot array;

FIG. 31( d): Combination of a frame-inversion drive and atwo-line-inversion (two-row-inversion) dot array; and

FIG. 31( f): Combination of a column-inversion drive and atwo-line-inversion (two-row-inversion) dot array.

Although not shown, as a pattern in which flicker polarity inversionbetween the pixels or dots is performed every two lines, regarding drivewave polarity and dot structure, it is also possible to switch thepattern of the drive inversion cycle and the dot arrangement cycle shownin FIGS. 31( b) and 31(f).

Specific examples are as follows:

(b′): Combination of a two-line-inversion (two-row-inversion) drive anda line-inversion (row-inversion) dot array; and

(f′): Combination of a two-line-inversion (two-row-inversion) drive anda column-inversion dot array.

Likewise, when n is 3 or greater, it is possible to invert flickerpolarities between pixels and dots every n lines. When n is 10 orsmaller (preferably 5 or smaller), interference with checkerboardpatterns can be prevented while reducing flicker, obtaining the sameeffect achieved by inverting flicker polarity distribution every twolines

Embodiment 15

The present embodiment relates to a color display device having the dotarray shown in FIG. 30 in which employs a drive method further enhancingthe flicker reduction effect.

In order to reduce flicker, like in Embodiment 14, it is preferable thatthe arrangement cycle of the regions showing the same flicker polarityrelative to a same voltage differ from the inversion cycle of a drivingvoltage.

Next, examples of the repeated patterns of dots (array of P and Q inFIG. 30) and desirable combinations with the inversion methods of adrive voltage will be explained. FIGS. 32( a) to 32(d) show, whenassumed the two adjacent dots have the different structures in withinpixel 91 as shown in FIG. 30, polarities of drive wave in an odd frame,the dot array and patterns of flicker polarity (odd frame) defined bytheir combination. Although not shown in the figure, an even frame has apattern of drive wave polarity inverted to that of an odd frame,resulting in having a pattern of flicker polarity inverted to that of anodd frame.

Like in Embodiment 14, an enhanced flicker reduction effect can beobtained in an arrangement in which the distribution of flicker polarityof pixels or dots is inverted every line.

Specific examples of such combinations are as follows:

FIG. 32( a): Combination of a line-inversion (row-inversion) drive and aline-non-inversion (row-non-inversion) dot array; and

FIG. 32( c): Combination of a frame-inversion drive and a line-inversion(row-inversion) dot array.

On the other hand, for example, when a checkerboard pattern appears on acomputer screen as a wallpaper, etc., it is preferable that, between thepixels or dots, flicker polarity be inverted every two lines to preventinterference between the a checkerboard pattern and the flicker pattern.Specific examples of such combinations are as follows:

FIG. 32( b): Combination of a line-inversion (row-inversion) drive and atwo-line-inversion (two-row-inversion) dot array; and

FIG. 32( d): Combination of a frame-inversion drive and atwo-line-inversion (two-row-inversion) dot array.

Although not shown, as a pattern in which flicker polarity inversionbetween the pixels or dots is performed every two lines, regarding drivewave polarity and dot structure, it is also possible to switch thepattern of the drive inversion cycle and the dot arrangement cycle inFIG. 32( b). Specific examples are as follows:

(b′): Combination of a two-line-inversion (two-row-inversion) drive anda line-inversion (row-inversion) dot array.

Likewise, when n is 3 or greater, it is possible to invert flickerpolarities between pixels and dots every n lines. When n is 10 orsmaller (preferably 5 or smaller), interference with checkered patternscan be prevented while reducing flicker, obtaining the same effectachieved by inverting flicker polarity distribution every two lines.

The display devices according to Embodiments 14 and 15 can be operatedin the same manner as shown in FIG. 28 described above. This allows adisplay of bright images with wide viewing angles and reduced flicker,when considering the entire screen or the regions comprising a pluralityof dots as a whole.

In Embodiments 14 and 15, the relationship between the drive wavepolarity and the dot array are explained with a dot taken as the unit;however, the preferable combinations of the drive wave polarity and thedot array described in the embodiments can also achieve the same effectswhen a pixel is assumed to be the unit. Furthermore, it is also possibleto consider the drive wave polarity or the dot array with a dot as theunit and the other with a pixel as the unit.

Embodiment 16

FIG. 33( a) is a sectional view of the display device according toEmbodiment 16 and FIG. 33( b) is a plan view showing the structure ofone dot of the array substrate. FIG. 33( a) is a view taken along theline DD-DD′ in FIG. 33( b).

FIG. 34 is an expanded sectional view showing the structure around aswitching element of a display device according to the presentembodiment.

FIG. 35( a) is a plan view showing a 4×4 dot section of pixels and FIGS.35( b) and 35(c) are schematic diagrams showing the polarities createdin the pixels. In FIG. 35( a), S1, S2, etc. indicate image signalssupplied to each pixel and G1, G2, etc. indicate scanning signalssupplied to each pixel.

In FIG. 33, 201 represents an opposing substrate, 202 represents liquidcrystal, 209 a represents an oriented film formed inside of the arraysubstrate 9, 209 b represents an oriented film formed inside of theopposing substrate 201, and 210 a, 210 b and 210 c represent colorfilter materials. Other elements which are identical to the elements ofEmbodiment 1 are identified with the same numerical symbols, andrepetitious explanation will be omitted. In the present embodiment, apixel electrode 1 is formed out of a metal material and an opposingelectrode 2 is formed of a transparent electric conductor.

In FIG. 34, 8 a represents an a-Si layer, 8 b represents an n+ type a-Silayer and 14 represents a contact hole formed in insulating layers 11 a,11 b.

The display device of the present embodiment is formed in the mannerdescribed below. On the array substrate 9, a first metal layer is formedof an opaque electric conductor made of Al, Ti or the like. The firstmetal layer is patterned into predetermined shapes to obtain a commonwiring 3 and a gate wiring 4. On the thus obtained layer, the insulatinglayer 11 a is formed, and then, a semiconductor switching element 5 isformed out of the a-Si layer 8 a and the n+ type a-Si layer 8 b on thepredetermined area of the insulating layer 11 a.

Thereafter, on the predetermined areas of the insulating layer 11 a andthe semiconductor switching element 5, a second metal layer is formedout of an opaque electric conductor made of Al, Ti or the like, and thenthe second metal layer is patterned into predetermined shapes to obtaina source wiring 7, a drain electrode 6 and a pixel electrode 1. On thethus obtained layer, the insulating layer 11 b made of SiNx or the likeis formed. The insulating layer 11 b also serves as an overcoatprotecting the semiconductor switching element 5.

Thereafter, the opposing electrode 2 is formed out of an ITO film, whichis a transparent electric conductor. In order to make the common wiring3 made of an opaque electric conductor and the opposing electrode 2 madeof a transparent electric conductor electrically conductive, a contacthole 14 is formed in the insulating layers 11 a, 11 b.

Then, on the array substrate 9 and the opposing substrate 201, orientedfilms 209 a, 209 b made of polyimide or the like are formed to alignmolecules of liquid crystal 202.

The opposing substrate 201 is arranged so as to face the array substrate9. On the opposing substrate 201, the red color filter material 210 a,the green color filter material 210 b, the blue color filter material210 c and a black matrix 211 are formed so as to have a predeterminedpattern.

The thus obtained array substrate 9 and opposing substrate 201 havetheir orientation directions formed in predetermined directions. Thesubstrates are bonded together on the edges by a sealer, and liquidcrystal 202 is sealed therein.

Operation of the display device is described below. The semiconductorswitching element 5 has its on-and-off status controlled by drivesignals supplied from the gate wiring 4. Then, an electric field isgenerated by a liquid crystal drive voltage applied between the pixelelectrode 1 and the opposing electrode 2; which are both connected tothe semiconductor switching element 5. By varying the orientationdirections of the liquid crystal 202, the brightness (lighttransmittance) of each pixel is controlled to achieve image formation.

In FIG. 33, d represents the cell gap, w1 represents the wiring width ofthe opposing electrode 2, w2 represents the wiring width of the pixelelectrode 1 and 1 represents the distance between the opposing electrode2 and the pixel electrode 1.

In the present embodiment, as shown in FIG. 33, it is assumed that thewiring width of the opposing electrode 2 is 5 μm (w1=5 μm), the wiringwidth of the pixel electrode 1 is 4 μm (w2=4 μm), the cell gap is 4 μm(d=4 μm) and the distance between the electrodes is 10 μm (1=10 μm). Inother words, it is designed so that the wiring widths of the opposingelectrode 2 and the pixel electrode 1 (w1, w2) become approximately thesame as the distance between the array substrate 9 and the opposingsubstrate 201, i.e., d (cell gap).

Regarding the shape of the electrode, for example, as shown in FIG. 33(b), preferable is a comb-like electrode in which the opposing electrode2 and the pixel electrode 1 are alternately arranged with a lateralelectric field generated between the opposing electrode 2 and the pixelelectrode 1. By employing the above described electrode arrangement, inaddition to the lateral electric field, the peripheral electric fieldsof the individual electrodes 1, 2 enhance the electric field strength onthe electrodes, rotating the liquid crystal. In the present embodiment,by forming the pixel electrode 2 out of a transparent conductivematerial, the electrode transmits light.

According to such an electrode structure, for example, by employing theliquid crystal 202 described below, it is possible to supply sufficientelectric field strength and drive the liquid crystal using a generallyapplied liquid crystal drive voltage (around 5V).

Specifically, as a liquid crystal material 202, a cyano-based liquidcrystal material containing a cyano-based compound in the range fromabout 10% to about 20% is used. Here, the optical-path difference Δn×d(multiply the cell gap d by the difference in the refractive index Δn)is assumed to be around 350 nm. It is also assumed that the liquidcrystal material used in the liquid crystal layer 2 have a splay elasticconstant K11 of 12 pN (K11=12 pN), a twist elastic constant K22 of 7 pN(K22=7 pN), a bend elastic constant K33 of 18 pN (K33=18 pN) and adielectric constant anisotropy Δe of +8 (Δe=+8). The dielectric constantanisotropy Δe and the bend elastic constant K33 are important factors inselecting the drive voltage applied to the liquid crystal. To lower thevoltage, it is preferable that the dielectric constant anisotropy Δe be+8 or greater and the bend elastic constant K33 be 18 pN or smaller.Cyano-based compounds are useful to prevent the localized accumulationof electric charge in the liquid crystal; however, having aconcentration thereof exceeding 35% may lower the reliability of thedevice because the ionicity is too strong.

Furthermore, since the pixel electrode 1 and the opposing electrode 2are crooked, the liquid crystal molecules rotate in two directions.Therefore, differences in color observed from different viewing anglescan be eliminated, obtaining a panel structure exhibiting littlevariance in color when seen from variable directions. Not shown in thefigure, however, if the source wiring 7 and the black matrix 211 areformed into crooked shapes having the same crooking angles as theopposing electrode 2 and the pixel electrode 1, the increase in areawhich blocks light caused by the crooked shapes of the electrodes 1, 2can be offset, obtaining a liquid crystal display device exhibiting afurther enhanced aperture ratio.

The advantages achieved by the display device of the present embodimentwill be described below. FIGS. 36( a) and 36(b) show the lighttransmittance properties of a pixel portion in a display deviceaccording to the present embodiment. In this figure, the pixelelectrodes (opaque) 1, 1, the opposing electrode (transparent) 2 and therelative brightness distribution (transmittance distribution) in theaperture are shown. FIG. 36( a) shows the case where a positive imagesignal is applied to the pixel electrode 1 and FIG. 36( b) shows thecase where a negative image signal is applied to the pixel electrode 1.From the figures, it is understood that the light transmittanceproperties are changed by the polarities of the liquid crystal drivevoltage, causing flicker polarity (light or dark polarity). As describedabove, the light transmittance properties are changed by the polaritiesof the liquid crystal drive voltage, and therefore the frame-inversiondrive whereby the polarity is inverted every frame causes flicker. Inthe H-line inversion drive in which a drive voltage polarity is invertedevery line or the V-line inversion drive in which a drive voltagepolarity is inverted every column, when a specific pattern such as avertical line or a horizontal line is displayed, it appears on thescreen as vertical stripes or horizontal stripes.

Therefore, the drive method employed in the liquid crystal displaydevice of the present embodiment is the 1H/1V line-inversion drive (alsoreferred to as the dot inversion drive) in which the polarity inversionof the pixel voltage is performed every line and every column as shownin FIG. 35( b). As an alternative, the 2H/1V line-inversion drive asshown in FIG. 35( c) in which polarity inversion of the pixel voltage isperformed every two lines and every column can be employed.

In the 1H/1V line-inversion drive shown in FIG. 35( b), when a patternof vertical lines or horizontal lines are displayed, the brightnessdifference between the positive and negative polarities are cancelledbetween two adjacent pixels, and thereby apparent flicker can becancelled. On the other hand, when a checkerboard patter is displayed,the 2H/1V line-inversion drive shown in FIG. 35( c) is preferable.According to this method, even in a checkerboard pattern, the brightnessdifference between the positive and negative polarities can becancelled, and thereby flicker does not appear on the screen. The sameeffect can be achieved by employing the 1H/2V line-inversion drive.

In the present embodiment, inversion of drive voltage polarity isperformed with the dot taken as the unit; however, it is also possibleto perform inversion of the pixel voltage polarity in the manner asshown in FIG. 35( b) or FIG. 35( c) when a pixel composed of red, greenand blue dots is assumed to be the unit. This arrangement isadvantageous in that color distortion can be prevented even in halftonedisplay which tends to be adversely affected by the difference betweenthe properties of brightness and voltage, since the properties of eachdot in a pixel can readily be balanced.

The conventional drive frequency for a frame is 30 Hz; however, apparentflicker can be cancelled by applying a frequency of 60 Hz, since even ifthe brightness differences caused by polarities are generated, the humaneye cannot recognize them at a frequency this high. This is also true inother embodiments.

Embodiment 17

FIG. 37( a) is a sectional view of the display device according toEmbodiment 17. FIG. 33( b) is a plan view showing the structure of onedot of the array substrate. FIG. 37( a) is a view taken along the lineEE-EE′ in FIG. 37( b).

FIG. 38 is an expanded sectional view showing the structure around aswitching element of a display device according to the presentembodiment.

FIG. 39( a) is a plan view showing a 4×4 dot section of pixels and FIG.39( b) is a schematic diagram showing the waveform of image signalapplied to each pixel shown in FIG. 39( a). In FIG. 39( a), S1, S2, . .. indicate image signals supplied to each pixel, S1′, S2′, . . .indicate compensated image signals supplied to each pixel and G1, G2, .. . indicate scanning signals supplied to each pixel.

In the present embodiment, both the pixel electrode 1 and the opposingelectrode 2 are made of transparent electric conductors. In otherrespects, the configuration thereof is the same as that of theEmbodiment 16. Therefore, the elements which are identical to theelements of Embodiment 16 are identified with the same numericalsymbols, and repetitious explanation will be omitted.

The display device of the present embodiment is formed in a manner asdescribed below. On the array substrate 9, a first metal layer is formedout of an opaque electric conductor made of Al, Ti or the like, and thefirst metal layer is patterned into predetermined shapes to obtain acommon wiring 3 and a gate wiring 4. On the thus obtained layer, theinsulating layer 11 a is formed and a semiconductor switching element 5formed out of an a-Si layer 8 a and an n+ type a-Si layer 8 b isobtained on the predetermined area of the insulating layer 11 a.Thereafter, on the predetermined areas of the insulating layer 11 a andthe semiconductor switching element 5, a second metal layer is formedout of an opaque electric conductor made of Al, Ti or the like, and thenthe second metal layer is patterned into predetermined shapes to obtaina source wiring 7, a drain electrode 6 and a pixel electrode 1. On thethus obtained layer, the insulating layer 11 b made of SiNx or the likeis formed. The insulating layer 11 b also serves as an overcoatprotecting the semiconductor switching element 5.

Thereafter, on the insulating layer 11 b, the pixel electrode 1 and theopposing electrode 2 are formed out of an ITO film, which is atransparent electric conductor. The opposing electrode 2 is connected tothe common wiring 3 through a contact hole 14 formed in the insulatinglayers 11 a, 11 b. The pixel electrode 1 is connected to the drainelectrode 6 through a contact hole 13 formed in the insulating layer 11b. Instead of forming the pixel electrode 1 and the opposing electrode 2on the same layer as in the present embodiment, it is also possible toprovide another layer and form the electrodes on separate layers.

Then subsequent production steps are the same as those of Embodiment 16.In the thus obtained display device of the present embodiment, both thepixel electrode 1 and the opposing electrode 2 are transparent,realizing a display device with an enhanced actual aperture ratiocompared to that of Embodiment 16.

The advantages achieved by the display device of the present embodimentwill be described below. FIGS. 40( a) and 40(b) show light transmittanceproperties of a pixel portion in a display device according to thepresent embodiment. In this figure, the pixel electrodes (transparent)1, 1, the opposing electrode (transparent) 2 and the relative brightnessdistribution (transmittance distribution) in the aperture are shown.FIG. 40( a) shows the case where a positive image signal is applied tothe pixel electrode 1 and FIG. 40( b) shows the case where a negativeimage signal is applied to the pixel electrode 1. From the figures, itis understood that the light transmittance properties are changed by thepolarities of the liquid crystal drive voltage, causing flicker polarity(light or dark polarity). In FIG. 40, there are two pixel electrodes 1and one opposing electrode 2. Therefore, even if both electrodes aretransparent, the displayed images become brighter in the case (b) wherethe pixel electrode 1 has a relatively negative voltage. This phenomenonoccurs because of the difference in numbers and areas between the pixelelectrode 1 and the opposing electrode 2.

In the present embodiment, as shown in FIG. 39, the difference inbrightness between the positive and negative polarities can be cancelledby supplying brightness compensation signals S1′, S2, . . . in additionto general image signals S1, S2, . . . . Specifically, when a positiveliquid crystal drive voltage is applied to the pixel electrodes 1, 1, asshown in FIG. 39( b), compensation for the image signal is performed byadding brightness compensation signals +S1′, +S2′ . . . to image signalS1. Thereby, the variance in the electric potential of a liquid crystaldrive voltage is increased and the displayed image becomes brighter. Asa result, as shown in FIG. 40( a), the light transmittance propertychanges from the condition without brightness compensation signal,represented by the solid line, to the condition with brightnesscompensation signal, represented by the broken line.

On the other hand, when a negative liquid crystal drive voltage isapplied to the pixel electrodes 1, 1, as shown in FIG. 39( b),compensation for image signal is performed by adding brightnesscompensation signals −S1′, −S2′ . . . to image signal S1. Thereby, thevariance in the electric potential of a liquid crystal drive voltage isdecreased and the displayed image becomes darker. As a result, as shownin FIG. 40( b), the light transmittance property changes from thecondition without brightness compensation signal represented by thesolid line to the condition with brightness compensation signalrepresented by the broken line.

By increasing or decreasing the transmittance properties by supplyingbrightness compensation signals, the variances in brightness when apositive liquid crystal drive voltage is applied and when a negativeliquid crystal drive voltage is applied can be made approximately thesame.

It is preferable that the brightness compensation signals S1′, S2′ . . .be controlled so that an appropriate voltage is supplied based on theratio of the area of between the pixel electrode 1 and the opposingelectrode 2, which are both formed out of transparent conductive layers.Specifically, the variance in brightness caused by the polarity of aliquid crystal drive voltage can be cancelled if the area SA of thetransparent pixel electrode and the area SB of the transparent opposingelectrode 2 are the same. When SA and SB are different, the variance inbrightness caused by polarity remains. The more the ratio of SA to SBmoves away from 1, the greater the variance in brightness is. Therefore,it is preferable that the variance in brightness be cancelled bysupplying an appropriate compensation voltage obtained based on acalculation of how far away the area ratio is from 1. Having thisarrangement allows a flicker reduction by canceling the variance inbrightness caused by polarities regardless of the number of electrodes.

In the present embodiment, both the pixel electrode 1 and the opposingelectrode 2 are transparent; however, even if only the opposingelectrode 2 is formed out of a transparent conductive layer like inEmbodiment 16, the same effect can be achieved by adding brightnesscompensation signals.

It is also true that in the present embodiment, like in Embodiment 16,the flicker reduction effect can be enhanced by employing thedouble-speed drive method which has a drive frequency of 60 Hz orhigher.

In Embodiment 16 and the present embodiment, a-Si (amorphous silicon) isused for forming a semiconductor switching element 5; however, use ofp-Si (polysilicon) or the other semiconductor layers can also achieve asimilar result. This is true also in the other embodiments.

In Embodiment 16 and the present embodiment, there are explanations ofcases where the pixel electrode 1 and the opposing electrode 2 arecrooked; however, the actual aperture ratio can be enhanced regardlessof the electrode shape, allowing use of linear electrodes, U-shapeelectrodes or others. This is true also in the other embodiments.

Embodiment 18

In the embodiments descried above, a rectangular dot was taken for theexample as the display unit, and the cases where the dots are arrangedin matrix are explained. However, the advantage of the present inventionis satisfactorily achieved even when a display unit is not a rectangulardot or the display units are not arranged in matrix.

To be more specific, the present invention can be applied to a structurehaving elements whose functions are substantially the same as those of apixel electrode and an opposing electrode even if the elements are notcalled by such names. Such examples include a circular-graph-shapedindicator I as shown in FIG. 41 for use in several kinds of meters and asegment display as shown in FIG. 42 for use in display of numericalcharacters or the like. By structuring each display block B and eachsegment SG based on the schemes described in the embodiments of theinvention, it is possible to cancel flicker in the blocks B and thesegments SG. As a result, an excellent display with a wide viewingangle, satisfactory brightness and reduced flicker can be obtained.

Also in a liquid crystal display device having a different arrangement,by structuring display units that perform the same kind of display basedon the schemes described in the above embodiments, it is possible tocancel flicker within each display unit. Thereby, an excellent displaywith a wide viewing angle, satisfactory brightness and reduced flickercan be obtained.

Also in the case where the whole surface of a wide image is controlledby a single signal such as in shutters for lighting or blinds forwindows, with assuming it to be one display unit, by structuring thedisplay unit so as to have two flicker polarities based on the schemesdescribed in the embodiments of the invention, flicker can be cancelledin each display unit. This achieves light control with reduced flickerand without being affected by a variance in the observation direction.

Other Embodiments

In the display devices according to the embodiments described above, itis preferable that, in one dot, the total number of the pixel electrodes1 and the opposing electrodes 2 be an odd number and the number ofintervals between the pixel electrodes 1 and the opposing electrodes 2be an even number. For example, in the structure of Embodiment 1 shownin FIG. 1 and that of Embodiment 5 shown in FIG. 5, by arranging thenumbers of the electrodes and the intervals therebetween as above, thecomposition of a dot becomes almost symmetrical in the left and theright halves, the flicker reduction effect can be enhanced. This is alsotrue in the arrangements of Embodiment 9 shown in FIG. 25 and Embodiment10 shown in FIG. 23.

In the arrangements of Embodiment 5 shown in FIG. 10 and Embodiment 6shown in FIG. 14, it is preferable that the number of the opposingelectrodes disposed between the two source wirings be an odd number sothat one of the opposing electrodes is situated in the middle of the twosource wirings. Thereby, two dots can be separated by the opposingelectrode, enhancing the aperture ratio.

In the arrangements of Embodiment 7 shown in FIG. 16 and Embodiment 8shown in FIG. 19, it is preferable that the total number of opposingelectrodes in the dot be an odd number, and it is more preferable thatthe number be 5+4n (n is an integer), i.e., 5 or 9, etc. This allows thecomposition of the dot to become almost symmetrical in the left and theright halves, enhancing the flicker reduction effect.

In the embodiments descried above, IPS-style liquid crystal displaydevices are used; however, as long as they have an arrangementcomprising a pixel electrode and an opposing electrode on one substrate,there is no limitation on the style of the liquid crystal display used.

Furthermore, with respect to the materials of the pixel electrode andthe opposing electrode, they are not limited to a combination of atransparent conductive layer and a metal layer. For example, a material,even one which is not completely transparent, if it exhibits atransmittance at a certain level, has the effect of improving thebrightness of the display device. Therefore, such a material and a metallayer can be used in combination. A combination of two transparentconductive layers having different transmittances is also possible. Thisarrangement can further enhance the transmittance.

When performing reflective-type display, the present invention can beemployed in a display device comprising a combination of two materialshaving different reflectances or a display device having a reflectiveelectrode as a back side electrode and a transparent electrode as anobserver's side electrode.

In a liquid crystal display device, as described above, flicker tends tooccur in the case where some portion of an electric field has asplay-shape around an electrode, causing the flexoelectric effect, andthe case where electric fields become asymmetric in the left and rightelectrodes affected by a peripheral electric potential caused by someportion of a display unit having no electrode. The present inventionexhibits remarkable advantages compared to display devices having suchstructures.

An example of a display device having such a structure includes a liquidcrystal display device in which liquid crystal is driven by an electricfield substantially parallel to a substrate. To be more specific, anIPS-style liquid crystal display device in which liquid crystalmolecules respond only in the direction parallel to the substrate, anFFS (Fringe Field Switching) style liquid crystal display device, and anHS (Hybrid Switching) style liquid crystal display device are included.The above-described structures of the embodiments of the invention canbe applied to a perpendicular-oriented type liquid crystal displaydevice, in which liquid crystal molecules L are perpendicularly orientedas shown in FIG. 43( a) when a drive voltage is turned off and theorientation angles of the liquid crystal molecules L change along theelectric field generated between electrodes 21, 22 as shown in FIG. 43(b) when the drive voltage is turned on.

In an MVA (Multi-domain VA) style liquid crystal device, a splay-shapedelectric field is used when the orientation of the liquid crystal isdivided by the distortion of the electric field. Therefore, thearrangements of the present invention can be employed in areflective-type display or the like which uses electrodes havingdifferent optical properties.

Rod type low molecular weight compounds are generally used as the liquidcrystal materials in each embodiment of the invention. In order toobtain the desired properties, anywhere from a few to several dozenkinds of materials are mixed. There is no limitation on the materialsused; however, in order to reduce the flicker polarities, a mixturecontaining a compound having a wider end directed to the positiveelectrode side, which prevents the flexoelectric effect, is desirable.The compounds represented by general formulae (A) to (F) below arepreferable.

In the above general formulae (A) to (F), X and Y represent cyclichydrocarbon residues. Specific examples are aromatic hydrocarbonresidues (benzene ring), aliphatic hydrocarbon residues (cyclohexanering), and compounds in which some of the carbon atoms composingaromatic hydrocarbon residues or aliphatic hydrocarbon residues arereplaced by hetero atoms such as nitrogen or oxygen.

P represents central groups including ester groups (—COO—), etc. Pincludes something which directly connects the groups on both sides.

In the end groups, Cn can be F, CF₃, CHF₂ or CH₂F and CH₃ can beC_(n)H_(2n+1) (n is an integer from 2 to 20). These end groups areresponsible for changes in the properties of the liquid crystal such aselectric or optical anisotropy and the temperature in which it is arange forming liquid crystal.

The number of the cyclic groups contained in the core section enclosedby the broken line is three or less in practical applications; however,it can be greater than three.

As specific examples of the compounds described above, the compoundsrepresented the formula below are included.

1. A display device comprising: an array substrate; an opposingsubstrate facing the array substrate; and an electro-optic substanceheld between the array substrate and the opposing substrate, wherein thearray substrate is provided with: a plurality of gate wirings and aplurality of source wirings intersecting each other; a pixel electrodedisposed in each region defined by two adjacent gate wirings and twoadjacent source wirings; a switching element for switching a voltageapplied to the pixel electrode from the source wiring based on a signalvoltage supplied from the gate wiring; a common wiring formed betweenthe two adjacent gate wirings; and an opposing electrode beingelectrically connected to the common wiring and generating an electricfield for driving the electro-optic substance between the opposingelectrode and the pixel electrode whereto a voltage is applied, whereinthe pixel electrode comprises a first pixel electrode and a second pixelelectrode, and the opposing electrode comprises a first opposingelectrode and a second opposing electrode, wherein a first region isformed in which an electric field is generated between the first pixelelectrode and the first opposing electrode whose light transmittance islower than that of the first pixel electrode, wherein a second region isformed in which an electric field is generated between the second pixelelectrode and the second opposing electrode whose light transmittance ishigher than that of the second pixel electrode.
 2. The display deviceaccording to claim 1, wherein the first region and the second region areadjacent to each other.
 3. The display device according to claim 1,wherein a voltage is supplied to the first pixel electrode and thesecond pixel electrode from the same source wiring based on a signalvoltage fed from the same gate wiring.
 4. The display device accordingto claim 3, wherein the first region and the second region are formed ina single dot.
 5. The display device according to claim 4, wherein theinterface between the first region and the second region is located onthe common wiring, and the first pixel electrode is connected to thesecond pixel electrode and the first opposing electrode is connected tothe second opposing electrode through contact holes formed in insulatinglayers held in between.
 6. The display device according to claim 4,wherein the source wiring is disposed between the first region and thesecond region, and the switching elements are arranged so as tocorrespond to the first pixel electrode and the second pixel electrode,respectively.
 7. The display device according to claim 4, wherein aplurality of the first regions and a plurality of the second regions areformed and alternately arranged along the gate wiring in such a mannerthat groups of two consecutively identical regions are alternatelydisposed, and the interface between that groups of two adjacent firstregions and two adjacent second regions exists on the pixel electrode orthe opposing electrode.
 8. The display device according to claim 1,wherein a plurality of the first regions and a plurality of the secondregions are formed and arranged in a manner such that the flickerpolarity cyclically changes along both the gate wiring and the sourcewiring based on the prescribed voltage polarity applied to the firstpixel electrode and the second pixel electrode.
 9. The display deviceaccording to claim 8, wherein the flicker polarities are inverted atevery dot along both the gate wiring and the source wiring.
 10. Thedisplay device according to claim 8, wherein the flicker polarities areinverted at every plurality of dots along both the gate wiring and thesource wiring.
 11. The display device according to claim 1, wherein thefirst region and the second region each corresponds to a dot.
 12. Thedisplay device according to claim 1, wherein the first region and thesecond region each corresponds to a pixel composed of three dots of red,green and blue.
 13. The display device according to claim 1, furthercomprising storage capacitor electrodes electrically connected to thefirst pixel electrode and the second pixel electrode, each of thestorage capacitor electrodes is arranged in the first region and thesecond region, wherein the two storage capacitor electrodes are locatedon the common electrode or the gate wiring with an insulating layer orinsulating layers in between to form storage capacitor regions and thetwo storage capacitor regions have substantially the same capacity. 14.The display device according to claim 13, wherein the two storagecapacitor electrodes are made of the same material and havesubstantially the same surface area.
 15. The display device according toclaim 1, wherein the first pixel electrode and the second opposingelectrode are made of a transparent material and the first opposingelectrode and the second pixel electrode are made of an opaque material.16. The display device according to claim 1, wherein the area of thefirst pixel electrode in the aperture of the first region and the areaof the second opposing electrode in the aperture of the second regionare substantially the same.
 17. The display device according to claim16, wherein the first pixel electrode and the second opposing electrodehave substantially the same transmittance.
 18. The display deviceaccording to claim 16, wherein an opaque layer is formed on the opposingsubstrate for blocking light over some portion of the array substrateand some portion of the first pixel electrode or the second opposingelectrode is covered with the opaque layer.
 19. The display deviceaccording to claim 1, wherein drive voltages applied to the first regionand the second region have the same polarity.
 20. The display deviceaccording to claim 1, wherein the first region and the second regionhave substantially the same absolute value of brightness differencebetween the case where the pixel electrode has a positive electricpotential relative to the opposing electrode and the case where thepixel electrode has a negative electric potential relative to theopposing electrode.
 21. A display device comprising: an array substrate;an opposing substrate facing the array substrate; and an electro-opticsubstance held between the array substrate and the opposing substrate,wherein the array substrate is provided with: a plurality of gatewirings and a plurality of source wirings intersecting each other; apixel electrode disposed in each region defined by two adjacent gatewirings and two adjacent source wirings; a switching element forswitching a voltage applied to the pixel electrode from the sourcewiring based on a signal voltage supplied from the gate wiring; a commonwiring formed between the two adjacent gate wirings; an opposingelectrode being electrically connected to the common wiring andgenerating an electric field for driving the electro-optic substancebetween the opposing electrode and the pixel electrode whereto a voltageis applied; and an intermediate electrode disposed between the pixelelectrode and the opposing electrode, wherein the intermediate electrodehas a transmittance either higher or lower than both the pixel electrodeand the opposing electrode.
 22. The display device according to claim21, wherein the pixel electrode and the opposing electrode are formedout of the same material, and the intervals between the pixel electrodeand the intermediate electrode and between the intermediate electrodeand the opposing electrode are substantially the same.
 23. The displaydevice according to claim 21, wherein the intermediate electrode isresistively connected to the pixel electrode and the opposing electrode.24. The display device according to claim 21, wherein the intermediateelectrode is subjected to capacity coupling with the pixel electrode andthe opposing electrode.
 25. The display device according to claim 21,wherein the electric potential of the intermediate electrode becomes theaverage value of the electric potential of the pixel electrode whereto avoltage applied and the electric potential of the opposing electrodewhich functions as a standard electric potential.
 26. The display deviceaccording to claim 1 wherein the electro-optic substance is liquidcrystal.
 27. The display device according to claim 26, wherein analternating voltage is applied to the pixel electrode.
 28. A method ofdriving a display device having: an array substrate; an opposingsubstrate facing the array substrate; and an electro-optic substanceheld between the array substrate and the opposing substrate, the arraysubstrate being provided with: a plurality of gate wirings and aplurality of source wirings intersecting each other; a pixel electrodedisposed in each region defined by two adjacent gate wirings and twoadjacent source wirings; a switching element for switching a voltageapplied to the pixel electrode from the source wiring based on a signalvoltage supplied from the gate wiring; a common wiring formed betweenthe two adjacent gate wirings; and an opposing electrode beingelectrically connected to the common wiring and generating an electricfield for driving the electro-optic substance between the opposingelectrode and the pixel electrode whereto a voltage is applied, in thetwo adjacent regions each defined by two adjacent gate wirings and twoadjacent source wirings the transmittance of the pixel electrodedisposed in each region being higher than that of the opposing electrodedisposed in the same region and the transmittance of the pixel electrodedisposed in other region being lower than that of the opposing electrodedisposed in that region, said method comprising the step of invertingthe voltage applied to the pixel electrode for every predeterminedadjacent region.
 29. The method of driving a display device according toclaim 28, wherein the predetermined regions are adjacent to each otherin two directions, along the gate wiring and the source wiring.
 30. Themethod of driving a display device according to claim 28, wherein eachpredetermined region corresponds to a dot.
 31. The method of driving adisplay device according to claim 28, wherein the predetermined regioncorresponds to two dots adjacent in a direction either along the gatewiring or the source wiring.
 32. The method of driving a display deviceaccording to claim 28, wherein the predetermined region corresponds to apixel composed of three dots of red, green and blue.
 33. The method ofdriving a display device according to claim 28, wherein thepredetermined region corresponds to two pixels each composed of threedots of red, green and blue, adjacent in a direction either along thegate wiring or the source wiring. 34-35. (canceled)
 36. A method ofdriving a display device having: an array substrate; an opposingsubstrate facing the array substrate; and an electro-optic substanceheld between the array substrate and the opposing substrate, the arraysubstrate being provided with: a plurality of gate wirings and aplurality of source wirings intersecting each other; a pixel electrodedisposed in each region defined by two adjacent gate wirings and twoadjacent source wirings; a switching element for switching a voltageapplied to the pixel electrode from the source wiring based on a signalvoltage supplied from the gate wiring; a common wiring formed betweenthe two adjacent gate wirings; and an opposing electrode beingelectrically connected to the common wiring and generating an electricfield for driving the electro-optic substance between the opposingelectrode and the pixel electrode whereto a voltage is applied, thepixel electrode comprising a first pixel electrode and a second pixelelectrode, and the opposing electrode comprising a first opposingelectrode and a second opposing electrode, a plurality of first regionsgenerating an electric field between the first pixel electrode and thefirst opposing electrode having a lower light transmittance than thefirst pixel electrode being formed, a plurality of second regionsgenerating an electric field between the second pixel electrode and thesecond opposing electrode having a higher light transmittance than thesecond pixel electrode being formed, said method comprising a step ofinverting a voltage applied to the first pixel electrode and the secondpixel electrode based on the arrangement cycles of the first region andthe second region so as to flicker polarities cyclically change alongboth the gate wiring and the source wiring.
 37. The method of driving adisplay device according to claim 36, wherein said step of inverting thevoltage comprises the step of inverting the flicker polarities at everydot along both the gate wiring and the source wiring.
 38. The method ofdriving a display device according to claim 36, wherein said step ofinverting the voltage comprises the step of inverting the flickerpolarities at every plurality of dots along one or both of the gatewiring and the source wiring.
 39. The method of driving a display deviceaccording to claim 28, wherein the driving frequency of the voltageapplied to the pixel electrode is 60 Hz or higher.
 40. The displaydevice according to claim 21, wherein the electro-optic substance isliquid crystal.
 41. The method of driving a display device according toclaim 36, wherein the driving frequency of the voltage applied to thepixel electrode is 60 Hz or higher.